Yep, thats my boat in the avatar. When i got it, there was no engine and it needed alot of work. I fully disassembled it and started from scratch doing everything I could myself. The engine is a 4.25 stroked 454 thats .070 over, so it's at 498cid. The 2 bolt main wont really be a problem until you start making some bettter power or start pushing some higher R's. I'm guessing 500HP+ or 5000RPM+, i'm no engine expert so don't hold me to this. If you plan on making more power i wouldn't mess with the impeller until then. I still think you should find out though whats in it. With a cam be careful not to go too big, boats, especially jet boats are a whole different animal. I would maybe call Clay Smith and talk with him, If i remember correctly he has cams designed to work well with mild 454 BBC's

Clay Smith Cams 5870 Dale Street Buena Park, CA 90621. Telephone: 714-523-0530. Fax: 714-522-3315