I figured the bell housing would be exactly the same. In a hot rod I can swap a transmission from a big block to a small block. bell housing on a chevy motor are the same. I guess I did know I need to install brass freeze plugs. I don't know what the cam card is as I didn't build the motor. it has a lopey idle for sure, but I have heard boats sound the exact same. why cant I use the accessories like alternator, starter, ect? 383 has the high dollar aluminum pulley serpentine setup on it. I really thought I could pull the 454 out and drop the 383 stroker right in and buy marine manifolds and I would be good. I know my 383 has way more power than the 454, but doesn't sound like it is going to work like I thought. sounds like my best bet is to have the 454 crank and rods turned and reconditioned and rebuild the 454 and reinstall.
first, unlike a car, a boat bilge actually traps vapors, and using automotive accessories in a boat means you just built a bomb., marine stuff is designed to prevent fuel leaks and igniting of any leaks.
lopey idle usually means lots of overlap, cam centerline on a marine engine is such that there is little to no overlap. any amount of overlap and you start sucking water into the cylinders (reversion).
cam duration - anything more than 270 total duration with wet exhaust and you suck water into the cylinders (reversion)
your 383 is most likely built for high speed / high RPM street use and probably has over 10:1 compression, probably close to a 296 degree cam. absolutely wrong motor for a boat.
a stock 377 in a boat puts out 350hp at the crank and 320hp at the prop. with custom exhaust, proper cam, carb spacer, etc. 450hp is the max you can get out of a 377/383 with a wet exhaust system for a boat unless you bolt a supercharger on top. and that 450hp will be temperamental and not long lived.
what vintage 454? what heads?