Dudes! You were supposed to talk to me BEFORE I drove to BFE!!!
I know you are all Ford and Chevy guys, but we had awesome luck with the Olds 455 in the boat pictured above.
My man will post later and give you all the details @ the boat we looked at. We are reasonably sure someone pulled it off the bottom of a lake somewhere.
Damned if you do, damned if you don't....
You did not have "good luck" with the Oldsmobile, you had one that was built right, which in starting over is both somewhat expensive and time consuming to do from someones used problems. That is just my opinion.
We have had a couple of good Oldsmobile's, had a couple real pieces of crap too...

The reason to stick with a Ford or a Chevy has more to do with the vast availability of good used parts and know how than it is being a battle of the brands. If you like the Olds, by all means go for it, but it needs to be done right the first time to be successful, cheaper to build a 454 than a 455 because of the amount of marine 454's around, everybody built a marine 454, not so for the 455. As for the Ford, unless you have Ford connections, they are a little more pricey to build than the 454, but a great motor just the same.
To add to Ron's post...American Turbine is good stuff too....

GT