If you are a really good engineer (like you are) and you live in a reasonably dry climate then there is no reason why 50 year old airframes should not be fine.
Being in the USA also helps. One of the things which costs money in Europe is that there is no authorised procedure for replacing bushes which are push-fit inserted into aluminium brackets. You have to either buy the whole bracket with the bush (typ. £1000) or you do a job off the books whereby you either (a) ream out the bush a bit and machine up a new pin or (b) push the bush out and machine up a new one and just buy the usually cheap bolt which goes into the middle of it. Some 99% of airframe parts are trivial to fabricate if you have a lathe and possibly a turret mill, but cost a fortune to replace officially. Under the right regulatory regime you just machine them up and an A&P/IA signs it off.
The other factor is whether there is a CMM (component maintenance manual). If you are totally anal about it, no CMM means the component cannot be worked on at all. I bet the 50 year old planes in question here were flying before anybody could spell "CMM". On things like Spitfires (AIUI) you can fabricate replacements if you have the manufacturing drawings, and for a Spit they do exist.
But then a Spit is not on an ICAO CofA which alone makes a massive difference to what you can do. We need to be comparing like for like.
Here in Europe, EASA-reg, the flexibility is gone unless you do stuff off the books. Put that together with crap lubrication (just squirting an aerosol lube into the bearings/bushes, without dismantling them and cleaning them) and that's why people with 30 year old C152s may be paying £7k to get them through the Annual.