Re: what oil are you using?
I was using HPR15 for the first couple thou in my 351... I will be moving onto HPR30 now.
Penrite have a really good tech department, give them a call. I have talked with them a couple times and A motor with good ring seal, under heavy load but in good condition should be using HPR30. Nothing thicker. I mentioned to them the guide given on the bottle as You would be more incclinded to run 40 or 50 going off their's guides and they say thats just to cover a wide basis. which i can understand.
if pulling load, you know how good your motor cond. is, I would run HPR30..