Will any type of beef jerky work?
Or cut a hole in a tennis ball, It’s true, I saw it on YouTube! 
What always galled me was, there was the nag tone for the seat belts, but never a nag tone for leaving your headlights on.
I had the exact same car (well, a sedan, not a wagon) and two front lap belts actually were standard for the first time in '64, and I think you got two rear belts in the cushier trims. However, back in those days it wasn’t all that uncommon for people to cut the belts out of cars the minute they got them home!
Also, I don’t remember if this was a standard feature, but that car did have a sort of poor man’s cruise control where you dialed in a speed and it would make this godawful squawking noise at you exceeded it. I recall being annoyed you couldn’t set it over 90. 
[/end of car-reminiscing thread hijack]
It could easily be that it was only the rear seat belts that had to be added. Because retractable belts weren’t available, he also got these spring things to put on the belts. The spring would wind the belt out of the way when you took it off.
I forgot about the speeding nagger. That was an awful noise. Kind of a cross between a buzz and a shreak. There was a minimum speed for it, too. You couldn’t set it lower than, I’m guessing about forty. I always thought that was to prevent kids and idiots setting it at 24 just to mess with a driver that hadn’t noticed that it had been changed.
I think that was the last car that Dad put curb feelers on. I haven’t seen those in a long time.
It’s a joke, son!
I think you’re playing a little fast and loose with your definition of beef jerkey.
<snip>
I learned to drive in a '68 Le Sabre “hard top convertible.” Ooh, fancy vinyl seats! A pebbly-textured vinyl landau roof! You could (manually) roll down both the front & back seat windows and have this HUGE expanse of open window with no separator. So cool! And I miss wind wings! 
Yeah, you had to hold down the button to keep the door locked when you closed it, or lock it with the key from the outside. It definitely had seat belts (3 front & 3 back) and the front seats had non-retractable shoulder belts that folded up into little clips above the windows. I don’t think they ever left those clips. 
I remember that buzzy thing! That Buick was SO smooth that we’d be cruising at 80 down the freeway before we knew it. Had to set that buzzy thing at a reasonable speed as a reminder. And when the national speed limit got set to 55, oh man, that was TORTURE! :mad:
My '89 Accord had that feature. I liked it.
Oh yes it is. I wasn’t even alive for well over half of “the mid-80s”, and possibly almost all of it depending upon ones exact defintion of “mid 80s”.
Therefore we’re talking basically before known history.
Both of the above are partially correct, however, there’s more to it. What the OP is describing is a trick on how to lock the car without using the key.
If you push the lock button down and closed the door the lock will pop open. But if you hold the door handle in the open position - and then push the lock button - you will be able to lock the door without using the key.