glaze bust the bores, new rings reuse old pistons.
my practice is to reuse original stuff where ever possible.
If a thing is 50 years old, and only half worn, it follows that it will last much longer than you'll use it in another 50 years.
Replacement spares are often crap and very expensive.
I just bought a handful of small parts for my brothers TR6, screws, a gasket, set of clutch rubbers and so on... 50 quid,