I'd go for the HQ too - just because I've done so much work on them I don't even have to think. For nearly 30 years they were the car I laid a spanner on most often....not because they needed it,but because they were so common.
Not the VW Beetle - you had to pull the engine out to work on them...and then had to pull all the tinware off to get at anything.
Re the original post - it would have to be pushrod and rear wheel drive,points and carbed,manual trans...then you could keep it going forever. For me,although they are ohc,I'd go for a Mercedes as they are repairable for ever - oh,but I've already got one,although as a 1994 it's too late model with too many electronics.
I've done this with my motorcycle a few years ago - got a bike that is simple and easy to work on,parts still available,able to be modified...and reliable and fun to ride. A BMW Airhead.