Are you dumping the exhaust and water right out the end of the riser without any other hose attached? If so, that is your problem. Add some hose to it. In the boat, you have a piece of hose and a tip on the end of the riser to help with scavenging. If you have an engine that is close to reversion and you run it with the risers open, they will revert. You can add about a foot or 2 of exhaust hose and it should stop. I found this out the hard way once.
Eddie

Eddie is on point when he mentions the hose and tips. I had a lot of reversion on mine while running it on the test stand, but when I put the hose and tips on, it helped a lot. I think in my case the salisbury flappers on the ends of the tips helped to interrupt the back pulse of the exhaust. I still had enough issues to force me to modify my header collectors, and I am still scratching my head over that, as it is a fairly mild cam.

Since you are only seeing reversion with one engine, I don't know if this completely answers the question. Did you replace the timing chain in both engines? I wonder if a stretched timing chain could retard the cam timing enough to induce reversion on an engine that is on the edge.

A leakdown test might be in order, especially since it only seems to be an issue on the even bank of the one engine. If for some reason a valve is not sealing properly, it could induce reversion. It's possible for such a situation to not really show up on a simple compression test, but the leakdown will tell the tale.

Try Eddies advice.

I've seen where bravo setups with short tails, revert, where on TRS/SSM tails, it doesnt revert. Basically because the tails/hoses are longer, even if the water is introduced at the same distance from the riser to manifold joint.

Thank you all for the help. I tooks the hoses from the boat and installed some tips and it made a big difference. There was still a little reversion but it idled much better and after a carb adjustment it ran really good. I am going to throw them in the boat and try them this week. Just for fun I took the hoses and tips off again on the stand (after adjusting the carb and timing) and it began to revert again. I am happy with the easy fix just wish I would of found it sooner.

Great ideas thanks again!!!!!!!!!!!!!!!!!!!