I have recently purchased my first jetboat, a 1973 Mastercraft, with 455 olds and Berkely 12 jc pump. The boat is very solid, and needs cosmetic work. I have refurbished a few ski boats, so am familiar with boating. I practicaly grew up on the Salton sea in the 70"s! I have  had this boat about 2 weeks now and have had a chance check everything for the first time out. Last Sunday we took it out for about 30 minutes, and I am hooked! The boat is very almost identical to the Wreidt that Brad of SoCal is restoring. The boat rode great but rode with the bow up high, I may just not be used to this? What I am getting at is, I noticed Brad's had a small block chevy, I am curious as to how mine might do with a mild 350 chevy. I didn't buy this boat to race. I just want to make noise and pull the kids and wife on skis and tubes. The 455 has a crack in the block, but only seeped a little water out of it. I know it may only be a matter of time before I may need an engine. I dont believe the engine was maintained very well. I read a good post on here about someone else wanting swap from a 455, and have really thought about it. Just looking for opinions.