Speaking as someone who has driven both a '67 Coupe and '69 Grande about, here are a few random notes on 'Stangs. Some of the suggestions are if you don’t mind doing some restro-modding and not having everything stock, but they’ll make the car much nicer to have as a daily driver.
*Hit some of the classic car shows/classic car drive-ins in your area, and ask around for who they take their cars to.
*Seriously consider upgrading to at least disc brakes up front if it doesn’t already have them. It’s amazing the difference in stopping distance/power between the '67 (drums) and the '69 (disc/drums).
*Ignition: points or electronic? Both have their (dis)advantages, but the conversion from points to electronic made both the '67 and '69 less fussy to start up.
*Both the '67 and '69 we have had problems with running hot/overheating, especially in Summer stop-n-go traffic. Shoving in the best radiator that would fit and putting a shroud on the fan solved this.
*Check to see if/when the engine has been rebuilt, and if so, has it been tinkered with to make it run better on unleaded gasoline. We did this to the '67, and so far this car has been bullet-proof (knocks on wood) when it comes to gas. Crappy gas, winterized gas, gas with varying amounts of ethanol in it (not that 85% stuff though): the only difference has been lowered MPG and ‘oomf’ with occasional rough idle with sub-par gas. No problems with decent quality regular grade gas, higher octane isn’t worth it. YMMV! 
*Radio and sound system: if the one you find has the stock radio, you may be stuck with AM only unless you upgrade this. There are radios being made that replicate the look/feel of OEM ones and will fit in the dash without much difficulty.
*AC: does the car have it, and has it been converted to 134a refrigerant?
*Cup holders, or the lack thereof.
*About having a mechanic inspect the car… At the very least, you’ll want to have it done just after buying the car: this is the route you’ll have to go if buying the car remotely (seller out of area). And I’m not sure what the going rate for this is. Having one done before buying the car is a good thing: it can warn you of problems lurking in the wings and give you something to negotiate with. The fun part is negotiating who to take the car to, etc. I’d be leery of a seller who flat-out refuses to let the car be inspected under any circumstances: what are they hiding?
*And as Tuckerfan alludes to, be prepared to have a lot of random people comment on your car. And offer to buy it from you, no matter the shape its in.
On preview: wow, this is turning out longer than I thought. Better cut it off here before everyone falls asleep. (I know, too late!)
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