I had the same decision to make, so I want to remind you that it isn't just going with a diff motor. It will mean $$$ for new exhaust, intake, alternator, oil pan etc. Granted if you go BBC all these things are easily found, but they all add up the cost. Olds blocks are all pretty much the same, and if you already have forged pistons and a good crank then you are halfway there. Someone can probably post a link to Timm's article about how to build the Olds for long life in a boat, or call Tom at JBP or David at R&D and they can give you the info you need most. There are a TON of little things you can do to improve longevity, it all depends on how much you want to spend at the machine shop.
I admit there is a certain sense of satisfaction when your Olds outruns a Chevy but . . . that doesn't happen very often. In the end, I found a smoking deal on an Olds long block ($500) that had just been built with all the good parts from a member on here who had cracked his hull. Good luck with what ever you decide.
