Look at using an oil with ZDDP in it. It's a zinc-based anti-wear additive that helps lubricate our vintage beasts.

There are vintage specific oils you can purchase but they can be ridiculously expensive. I have heard diesel oils have the required ZDDP but you want to be sure not to get one with too high of a detergent level in it as that can be bad for the engine.

Alternatively you can buy a zddp additive. Maybe check at Lordco or your fav. parts supplier... or of course you can buy it on Ebay or Amazon.