So my 2002 Formula 292's 350 mags have 475 hours on them. I planned on doing a compression and leak down test, plugs, wires, etc. What else should i check? The boat is getting new exhaust and hydraulic steering so itll have some down time. Any input is appreciated!!!

You could do those things for piece of mind, but doing compression and leakdown tests on those motors is probably not necessary unless you've noticed a problem. Oil change, plugs, wires, cap and rotor are probably all they'll need. The 350 Mag so long as the manifolds are good, will run for a really long time. 475 hours is nothing on the valvetrain. If the manifolds are good, I'd leave'em be.

I agree, unless you hear something, or performance is down. Oil change, plugs, wires, cap and rotor and routine maitenance is all that is probably needed. Manifolds are sometimes a problem, but if freshwater run then usually not an issue. Many people put 1000 hrs without opening. Reliable setup.

There aren't any noises or anything out of the ordinary. I come from the hot rod world where every couple years I look over my engines and do a few test so it's just force of habit. The previous owner of my boat was extremely punctual and meticulous about maintenance, so I doubt I would find anything wrong but I'm a worry wart lol. I got 2 sets of IMCO powerflow manifolds with stainless tails from a boating buddy, which is the only reason the stockers are coming off.

The stock parts have caused more wasted engines that anything! You'll like the new exhaust.

Yes the weight reduction and slight performance gain with the powerflow is a win win. My 292 isnt quick to plane out so the less weight the better.