Double post

you really need to get a wideband 02 and see what you have at cruise wot etc, otherwise you are pissing in the wind...

Yes, but if you are burning all the pistons fed by the right venturi and none of the pistons fed by the left venturi 2 or 3 times, I would look into correcting carb issue before I had to replace 4 more burnt pistons.

be very hard to figure out which venturi is feeding what...things in the intake mixes far more than you would think

If plenum divider is intact, each side feeds either the upper or lower plane on the intake exclusively. If divider is gone, it is essentially a single plane intake.

What pistons? Brand, type and part #.
Cast, hyper, forged?

4 hrs time best in 3 attempts. JC Whitney pistons should last longer than that. And always 1-7-4-6 with dual plane intake? Left side of carb is lean.
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The answer is complicated at this point but when you repair the engine again have the engine builder dyno it and you will be able to isolate the engine from the fuel system in the boat. If your exhaust temps are within 1200-1300 degrees on the hot side and your BSFC is within the high .40s and low .50s you have no knock with the fuel you run the engine is ready for the boat. At that time you need a fuel press gauge in the boat to see if you're running out of fuel under low partial or wide open throttle. You can have simple things as a bad fuel pump a tank that doesn't have a good breather a plugged up or restricted fuel pickup in the boat. Also all the above with the carb and distributor. You can eliminate all the work with the dyno work to figure if its the tune or in the boat . Best of luck sincerely Laz Mesa