Re: 4.3 mercruiser to 350 converison
do a couple searches and some digging on here. number of people have done it and there's a ton of mostly very good information on here. I've only done this swap a few times now, once in a boat that took significant modification. Some others have more experience.
In general, most things will work depending on how much room you have and if there is easy rom to move your motor mounts forward (don't have to be new ones in most cases, just need to move them forward), al your electrical system, alternator, water pump, starter, trans cooler, pulleys, etc... SHOULD work, even the distributer (with different cap and rotor, module depenging on what you put in for an engine). the exhaust manifolds risers, etc.. are one of the things that won't work. don't trust a used set if you can help it and definately not unless you pressure check or have them checked.
In my experience it is not necessary to change the gear ratio - at least not right away. I've been running the original 1.8 gear ratio in my smaller boat on the advice of the engine builder, and have been very pleased with the result. I tried the lower ratio and switched back. the difference in pitch between 1.81 (probably your current ratio) and 1.47 (the standard 350 alpha gear ratio) is only about 4" in prop pitch. Granted, you're not going to find cheap aluminum props in the 24-26" range you'll probably need with the 1.8 gear ratio and 350, but there are a number of (really) good stainless ones around both new and used. just my experience...
Good luck with it!
