Back round... Motor is 97 model 525 SC. Started popping thru carb under acceleration (trying to get on plain).
Checked valvetrain first. Everything moving fine.
Swapped carb - same problem
Swapped distributor, coil, cap & plug wires- same problem
New plugs - same problem
new fuel pump - same problem

Then (finally) stepped back and ran compression check. #1 cyl 138 psi, #2 cyl 135 psi...... #5 & #7 cyl 0 psi. Double checked valve train and valves "appear" to be getting normal full lift. At this point I am thinking it's a head gasket blown between #5 & #7 cylinders. Can anyone think of either a way to verify this, or some thing else that would cause this, or other things i should look for while replacing the head gasket.

How many hours?

You have an obvious no compression problem but for what its worth mine started running bad like that before I tore it down and it ended up being a bad sea water pump...the cam inside that drives the fuel pump got flat and I was losing fuel pressure...

I bring this up because hopefully you didn't have the same issue and run it lean and the no compression is actually 2 bad pistons or bad valves.

With the valves closed pressurize #5 and see if air come out #7 spark plug hole

a leakdown test will solve your mystery

Winner, winner, chicken dinner....... Blowing out as fast as it goes in. Thanks a ton for the tip!

About 250 hours. I will look at pistons also when i pull the head off.

Might as well do a cam swap, up the compression, add a chiller, bigger blower, swap the 454 for a 540, upgrade ignition, aluminum heads.....see how that snowballs hahahahaha

In all seriousness tho...check the deck surface and head mounting surface for degradation from the head gasket being bad. Doesn't take much to start eating away at those surfaces. Hopefully it'll be a quick head gasket change and back on the water in no time!! Good luck!!

Oh, believe me, I know that snowball..... And would if it wasn't a twin snowball. That and I've only found one chick that will ride with me at 90+...... Rest are booze cruise speed. Might as well put a 25 honda on the back as far as they concerned. LOL
Yeah, the heads were just done right before I bought it, so hoping maybe just an oops oversight kinda thing. Definitely gonna check it all out when I get the head off

If its that bad, I think you are going to have head or block issues. Hopefully not, but be prepared.