Classic/Antique Car Repair: Engine oil for my 1951 GMC pickup, hd oil, gmc pickup

Question
I have just gotten a 1951 GMC pickup with the original
208 6 cyl. engine.  It has unknown mileage but the guy that
I purchased it from said it had been rebuilt.  He had been
using 30 wt. HD oil.  Should I continue using 30 wt. HD oil
or would something else be better.  It doesn't smoke at all
and runs good.  Thanks,  John

Answer
John, this is like asking which is better, chocolate or vanilla. If the engine is running well and the oil pressure is ok, and it is not using oil, then the old if it ain't broke saying applies. It appears to me that 30 weight HD is a good choice.
Brad