I would check voltage at the coil to see if that’s the issue. You have

swapped the : carbs , coils , ignition modules but not the distributors

replaced :the wires and plugs

checked: physical positioning of TDC per timing mark , ignition timing , float level and mixture screw, fuel flow

after rereading moving things back and forth produce no change , did you move the distributor to the bad running engine? You can use a capped off vacuum port to check the vacuum, does the choke open all the way,I assume electric choke, does it have 12 volts ? How about smoke testing the bad engine for a vacuum leak? Did also pull all 8 plugs? , keep them in order and see how they look

Hi... found out what the problem was. The guys that "fixed" the engine just did not tighten the rockers... got it working, but now a new set of problems. I will start another thread with new problems

If the exhaust is exclusively through the prop, check to see if the flappers are intact in the top of the Y pipe. I have seen 2 boats where the flappers gave away and caused a restriction. The first time we found it, the boat had been to several reputable repair shops and was never diagnosed. That boat had a plethora of head scratching symptoms and once the flappers were removed it ran like new - maybe because everything else was replaced haha!

Would be a good idea, but it has silent choice, and new flappers down below.