A little throttle on start up shouldn't have thrown a piston into a spark plug. Keep us posted as I'm curious. Best of luck!

Ya have to know somebody with a leakdown tester.
If you pull the motor yourself as soon as it hits the floor slap the intake back on cover exhaust ports and pull all the freeze plugs and personally extract the crud that will be sitting in the bottom of that 502.

I have Dorr's Marine working on it now, Windham Maine. Complete rebuild should take 4-6 weeks. I dropped a exhaust valve into the top of the cylinder. The piston has a nice indent of it I'll try and post some pix. About all I can save is the block. I'm keeping it a 500. not giving it any extra HP. 15 years is a lot of wear and tear. Hopefully it will last that long again. Reading some threads that try and get 500 hours without going through the engine seems nuts to me. It would have cost about half to rebuild if I had caught it in time. I was considering sending it out to one of the top shops mentioned above, BIG props for Ron Potter,he answered his phone on a Saturday and called me back on Monday, but the freight and timeline didn't seem worth it at this point for me. We are keeping the engine pretty much stock, Tim's shop is an hour away and he was very well recommended by some big boat locals. Thanks again for all the help

When you say dropped a valve...did it crack and fall? Or did something else fail? Clips, etc?

Our 500 at 300 hours had terrible corrosion on valves. These 500's revert a little and that's the end result.

Good you found a shop. As for the hours had the other owners did the top ends 500 hours is easy. It's the valve train that fails and sounds like it did on yours.

Keep in mind most recommend redoing the springs at least at 250 hours. For the stock stuff anyway.

The stock HP500 cam is prone to reversion especially if you have the older style risers.
I would definitely get a different cam grind.

You're in very capable hands with Tim Dorr. He did the motors in my Cigarette and the motors in my last Cigarette. He's at the top of his game.