Tried to renegotiate down $7K in the price to account for top ends. Seller declined. So, I'm out. Thanks for the input all!

Good call. Might be as simple as a little corrosion (doubtful) however that’s a good number you negotiated for a piece of mind.

150-180 psi variance, up to 65% on a cylinder and not knowing where the leakage was coming from??? I'd have more confidence in the engines than the tester.

A stock 502 magnum will crank in the 155 psi neighborhood. That's an 8.8:1 motor with a [email protected] cam.

Upwards of 180 suggests oil in the cylinders artificially raising the psi.

I have to ask if the compression test and leak down were done on a winterized motor(s) or running motors after being warmed up and cooled down.
You need to run them up to operating temp, then Rev em several times, spin em up to 4000 or 4400 rpm. Then back to idle and let them cool down enough to pull plugs and run tests.
The reason is that fogging oil will screw with psi readings. The other reason is that carbon and fogging residue over a winter can Harden and prevent some valves from sealing as well as they should.
After you run it up to temp, Rev it some, then any partially sticky rings will be freed up, crunchy residue on valveseats will be hammered off, and any fluid/oil/whatever will be burned out of the combustion chambers.

Your wrench guys ought to know this. But sometimes you need to specifically ask...

I'm out of the deal at this point, and pretty comfortable with that decision, BUT, they're not stock 502s. They dynoed at 565 HP when originally built. So, it's likely the compression is a good bit higher than a stock 502 mag. I asked the seller if he knew the compression ratio and he did not.

Initially my impression of the boat was that this was a well loved and cared for "baby" but as things have unfolded I think it was an occasional toy that got hauled to the shop when something wasn't right, but didn't seem to get the love that I like to see in something I'm interested in buying.

Use a bore scope to take a look, first I'd take it for a good beating to dust off any rust and blow out any oil from winterizing.

I understand you have passed on the boat that you started this thread about. I just wanted to ask a question about it though.

Do you know which cyls were low?

Aren't cyls 7 & 8 susceptible to water intrusion from the exhaust? If so, isn't it possible the seats or valves could be damaged?

It was cyl 4 on one motor and 6 on the other. so, interesting that it's on the same side of each motor, but not sure what to infer from that.

I know you passed on this deal,and I get it, so this is just info for next one. I had the heads milled .020 on my 502mag with stock pistons and bore and it runs mostly 180 on compression check.

Good to know. These motors had Edelbrock aluminum heads, pretty big cams with over 0.600 lift, and had allegedly been refreshed twice since original builds. Too many unknowns and maybes.