Bamaro - My new variable DOHC engine is a flat tappet type, also.
You have rollers or flat tappets. [Unless you have a Desmodromic system.]
Gonz - Are you going to drive this car? 500 a year? 10,000?
For hard use I'd use a diesel oil in 15-40. Those engines were not lovers of thinner oils - not yet.
You could use a 5-30 for light driving here and there, with no great heat to deal with.
Oils were not that great then. They got better in 20 years. And now, oils are castrated, but have substitute methods of anti wear.
BTW, your cam and lifters will still wear somewhat. They wore then, and they'll wear now.