How do can you do a leak down if there's no compression in the cylinder, or did I miss something.

The leak down will isolate where the problem is resulting in the loss of compression. The air will escape either thru the intake, exhaust, or crankcase.

I understand how it works, but if there's NO compression you cant tell anything, could be a hole in the top of the piston, the OP said no compression not low

If there is a hole in the piston you will hear the air escaping from the crankcase (breather), instead of out the exhaust or through the carb if there were a stuck/broken valve. It might not tell you for certain that it is a hole in the piston versus a broken ring, but it would help to isolate the problem a little more and maybe tell you if the engine has to come out versus possibly pulling a head and fixing a valve.

I had a chunk come off of the ringland of #6 and it busted off a 1/8" piece from the intake valve. Boat ran fine from idle up until about 3800 RPM. If you tried to lean on it, it would backfire through the carb. I originally thought I had a weak fuel pump causing a lean pop, or an ignition issue. Only after a compression test showed about 80 PSI in #6 did I realize I had a major issue. When I pulled it apart I found a chunk our of piston #5 as well. Compression was fine in that cyl.

If you are truly getting zero compression it almost has to be a really big hole in a piston or valve.

I would guess warped head and blown gasket.

I think my heads warped for posting on here

Let us know please, the final verdict

What's actually involved? Money. Lots of money....

i am not sure how an engine can run fine when it has a dead cylinder.