Joe, you'll have read it somewhere else no doubt, but as you'll be looking at older cars, the most important thing is condition, not mileage or age.
The only trouble is - much of the bits that are most important condition wise are hidden away.
Open the doors and try lifting them at the catch end. There will be some play - make sure the play is in the hinges, not the wood uprights the hinges fasten to. If you can, lift whatever is covering the rocker panels (inner sills) and check the condition of the wood.
Check around inner arches, plywood is prone to rot in the rear arches and part of the wood frame. Take a good look at the gusset (tri-angulation) plates that strengthen the chassis rails forward of the bulkhead (firewall) - rust can get between them and the chassis legs leaving little support and causing lots of front end wobbles (don't ask how I know

). You can always replace with the later (longer) plates to give better support.
Check condition of inner valances at the front and tinwork generally.
Usual checks of older engine for smoke etc. - but you'll be familiar with that being "in the trade".
Most of all - GOOD LUCK with finding the car that suits you - and do tell us all about it, with lots of

when the right car has chosen you (it does happen!

).
Oh, and welcome to the forum
