Do people still worry about the miles on a vehicle? I always thought that was silly and have never cared. First thing I look for is the type of vehicle I want. Has to be an old Ford, generally mid 70s or older car or '86 and older truck and no electronic controls, then furthermore must not be subject to any emissions laws in NJ. That leaves diesel trucks '86 and older or cars early 70s at the newest.
Often it's hard to find the year and model I want so I'm happy to find anything within a reasonable distance of a few hundred miles and I've already made compromises because so few of anything have a manual trans right off the bat. Things I won't touch no matter what are power windows, locks, stuff like that. Don't want to deal with converting that stuff (door panels and misc hard to find parts). Won't do 4 doors, though I broke that rule with this truck, but I figure trucks are different and to get a Supercab like I wanted would mean a Dana 60 swap. Wasn't worth a grand or two and the time involved to swap.
So anyhow, after I've found something that meets those criteria, it's something I'd be happy with potentially indefinitely so long as the laws where I live don't subject it to inspection or other legal hoops to jump through and fines to pay. At that point we've got a body style I like and no legal issues, inspection begins with rust issues. Any rust? Surface or rot? Where? Is it a nice looking bucket of bondo that will only look nice for a couple month before it all cracks and falls apart or starts rusting again? Do I feel like taking the time to repair that? etc... If that checks out, does it run and drive? It so we got a winner. Obviously there's a little more to it and negotiate on price depending on the amount of rust or how I perceive drivetrain condition (do I need to build an engine? Swap to a manual trans? etc...). Little maintenance stuff like fixing typical wiring issues, all new brakes, fluids, seals, wheel bearings, ujoints, etc. I just assume to be required on anything 30+ years old unless explicitly stated it has recently been done. That stuff is cheap and easy and if it runs and drives well you can usually do most of that on your own schedule.
Mileage is more of a curiosity because you never know for sure and it means so little because in 30+ years it could have been taken good care of or abused by so many people. If you like the truck (or any vehicle) then there's no reason to sell so give it whatever it needs whenever it needs it and you'll save tens of thousands over buying a new car, and have a much nicer vehicle than some disposable econobox.