Engine replacement 305K to 350

I have rebuilt a 350 from blazer it rotates looking at rear of engine , flywheel to left . I have trans from boat CC , rotation on cover saids right hand rotation ; going to be installed in 1976 CC catalina express.. what is wrong????

Twin engine boats need to have the props rotate in the opposite direction. There are two solutions to this problem...
a) Have engines that turn in different directions
b) Have engines that turn in the same direction, but have transmission take care of the opposite rotations.

Am I right to assume that you are thinking about installing a rebuilt truck engine in a boat?

The engine from the Blazer would be Standard Rotation.... i.e., LH.

Not all In Board transmissions are capable of reversing the roation with the intent of this being your FWD propulsion.
I'd say that this needs to be determined first.

If you are considering using an automotive engine in a marine application...don't! There is a lot of difference in the way marine engins are built. Think about driving your truck around pulling a heavy trailer at 3500-4000 RPM's all day every day and that will be simalar to the load on a marine engine. I know a few people who have tried it and the engines didn't last more than two seasons.

If you have the original engine, get a new marine long block from someone like Jasper and swap your components (starter, alternator, etc). Even these are different for marine applications as they are designed to eliminate open sparks which could cause a big problem in a boat. The fuel pumps are designed to keep raw fuel from leaking into the bildge as well if a seal fails.

Just my .02 worth.

Dave