Rob, I could only say that the 350 gets it's displacement from more than the size of the piston, as you probably know. I will check my reference tonight to see how close the bore is in a 350 vs a 330. As another option you might check this spot out and ask "Blownolds". He is on the site in the link below as well as other Oldsmobile performance sites. He might be able to help you out too.
http://www.jalopyjournal.com/forum/s...highlight=olds