I converted a truck from automatic to stick. That was easy because standard parts fit, and they made the trucks in both stick and automatic.
I found '73 Buick Centurion. I’ve been looking for a while. I’m going to buy it and start restoring it.
It’s got the 455 engine.
I’m considering converting it from an automatic to a stick.
I was wondering if anybody knew of any conversion kits out there that might serve the purpose?
The Centurion, like the Riviera, Electras, Eldorados, Delta 88s and other land-barges of their ilk, never came in stick-shift models.
It won’t be impossible, but it’ll require some custom fabrication, rather than mere transplanting of stock parts.
The easiest way would be to spring for a complete hydraulic clutch assembly, from Summit or Wilwood. You’ll have to manhandle a lot of junk out of the way under the dash to make room for the pedal assembly, plus knife a hole in the firewall in the right spot for the master cylinder. (Which will, of course, have to clear the massive brake booster on the engine side of the firewall.)
After that, you’ll just need a BOP-C manual-trans bellhousing, the tranny you’re going to use, an extended driveshaft, cut a hole in the floor to clear the shifter (and hope it clears the seats) and very likely you’ll have to have the Buicks’ crankshaft machined for a throwout bearing.
Other than that, it’s easy. 
IIRC the 1970-72 Buick GSX musclecar had a 455 w/a 4-speed option. You might be able to use that bellhousing, clutch and tranny w/a fabricated driveshaft, aftermarket shifter and generic hydraulics.
Boy, Scylla, wish you were in Kansas City, you’d get as many hours of free help outta me as you needed. I’d LOVE to help with something like that! 
–Tim
Beatle- If you can find the 4-speed and accessories for a 455 GSX, I’d hate to see 'em wasted on a Centurion mod. I can name two GSX restorers who’d fork out big cash for the right parts.
You’re looking at a couple of grand easy- they only made something like 2,300 GSXs, as I recall, and fewer than half were sticks.
Wasting the parts on this kind of mod would be like finding an Olds W-27 and sticking it under a $500 '76 Caprice Wagon.
Now, if you happen to have a stash of Buick parts, let me know if you run across a set of Stage IV heads… I’ll pay shipping.
Actually, Doc, I had considered adding something to the effect of, “if you could spirit such artifacts away from the GS crowd.”
Really though, the bellhousing would be the big threshhold to cross, wouldn’t it? Perhaps a replacement (who made the grenade-proof bellhousings? B&M? B&H? Sorry - it’s been a long time). The tranny was likely a widely used GM 4-speed (T-10?). So, I would think bolting up to the 455 block would be the big part of the journey. The driveshaft (unless Scylla is incredibly lucky) would have to be fabricated, or modified - not a big deal.
All of the rest could be done with aftermarket parts.
B&M.
If all else fails, try Advance Adapters.
The driveshaft is the least of my worries. You guys are giving me some great ideas. Please keep going.
I’m not worried about the hydraulics, the clutch pedal, or the shifter. I’ve never done anything except from a kit or from standard parts. Nevertheless, I’m sure I’ll manage to get the clutch pedal, linkages, hydraulics, and shifter installed without too much difficulty. The front seat is a two part bench, which could be removed for buckets and a center console to handle the shifter.
Getting a new drivetrain is no problem. I had to do that for my truck, and I know a guy who will cut and balance them reasonably.
My main concern is the transmission and bell housing. Chances are, if I can’t do it with readily accessible parts, I’ll just leave it as a slushbox.
Beleive it or not, I’m buying the car for $1,500. The convertible top is shot, but it’s rust free other than for a little bubbling near the trunk.
I happen to know the 455 is worth more than that by itself.
Aren’t Advance Adapters truck transmissions?
I know it’s impolite to split hairs, but lest we have someone getting funny looks at the parts counter…don’t you mean pilot bushing/bearing?
For those who don’t know, (not the Doc, he knows this) the throwout bearing goes on the input shaft of the transmission, and transmits the motion of the clutch fork to the levers in the pressure-plate.
You may find it ironic that I have a $400 '80 Caprice 4-door with about 400 ponies of 4-bolt SBC under the hood. Not a '76 wagon…not a W-27…but a beater to be sure, and a Mustang killer to boot.
Yes it’s weird. That’s my nature. The weirder the better. It gets double takes. Sometimes it makes people jump when I fire it up. It has a high grins-per-gallon ratio.
beatle - Lakewood, McLeod.
No, I insist you try to machine it for a throout bearing.
(I just want to see what happens! )
Hee hee… Yah, pilot bushing. You’re exactly right on the throwout description. Hey, I had about four free minutes to surf…
Yes, I think the bellhousing will be the sticker. Only Cadillac never had some form of manual tranny behind the musclecar-era non-Chevy GM big-blocks. A bellhousing from/for a Pontiac, Oldsmobile or Buick (in all cases either big OR small-block, they’re all the same) will fit.
Barring that, since of the three, none were real prolific manual-tranny users, and in all cases you’ll end up with an aluminum housing, you can ring up your local race shop and ask around for a bellghousing/scattershield. It’ll be steel, probably a near-universal fit, and about $300 and up.
Any decent tranny should work, 'cept maybe the generic Saginaw 3-speeds. A T-10 (or Super T-10) would be nice if you can find one, any of the Muncies, or heck, jump for a newer unit from NV and get an overdrive 4-speed.
As for Advance Adapters, they make damn near any adapter you need- Jeep tranny to Chevy truck transfer case, Ford tranny to Jeep transfer case, Toyota to Jeep, Toyota to Chevy, Chevy to Toyota… heck, there’s even Toyota-to-Toyota-to-Toyota, if you like having 235:1 low-range for your four-by.
You need a bellhousing though, not necessarily an adapter. Yes, they make bellhousing adapters, but to be honest, I don’t recommend them.
Scylla- Trust me on this: The clutch linkage will be FAR harder than you expect. The tranny and clutch, with the right parts, will be essentially a bolt-on. But the linkage will require at least some modification, and unless you plan on stripping the entire dash to a bare framework, it’ll be nasty, cramped work. AND, (I have a little experience here) if you DO do it with a stripped dash, you may guarantee that you’ll discover something kind of important, like say the speedomoter cable, or the left side of the guage cluster itself, won’t fit with the new bracketry in place.
Measure twice, lay it all out, go have coffe and think about it. Come back, measure three more times, consult an experienced professional, measure two more times, THEN cut.
Because you like the dirt, right?
For someone soon to be known as The Boy With The Spanner In His Head you sure have a strange interest in things mechanical.