90 4.3 omc shack/miss

[cuzzzintn]

Lets start with the first issue. Last year had boat docked and took on water around drain plug. Water got in motor. Drained motor and cousin tried to start before i got plugs out and there was water on top the pistons. Took to shop found a crack in 1 head so bought a used one and had both machined and new valves put in. Put back together and it runs great till around 2200 to 2400 rmp and then has a vibration or miss. Did a leak down test came out ok . Though a fire issue replaced cap rotor points plugs wires coil.. and rebuilt carb still same. Heard several things from diff people. Possible bent connecting rod. I figured if that would vibrate all the time. Also heard fuel issue. Im to the point i have no clue. Plus it has been at a shop for 1 1/2 months and they have no clue. Wants to pull motor this weekend and go through it just hoping to find something.. please help