Just pull 6 spark plug out, put air in the cylinder , if it comes out number 8 or number 4 you got the problem

Will do that tomorrow before I tear into anything.

Well tonight I did a leak test and confirmed the problem when air started coming out the adjacent cylinders.
Head gasket was blown between each cylinder. Good thing I ordered Fel-Pro gaskets and ARP bolts today just in case.

Cool glad you found the problem

i reccomend checking the block&head with a straight edge for warpage.

Most definitely. May even want to take that head in to see if it needs to be resurfaced. Kinda unusual it would blow between ALL the cylinders on that side. Need to get that head off and confirm your problem. I had one blow last year between 3-5. In my opinion I doubt you have any ring problems or damage from returning to the dock..

i have seen them get hot enough to blow the head gasket and put water in enough to milk the oil but nothing warped but it still needs to be checked.

A guy brought me a hp 500 carb motor that blew the head gasket between all the cylinders on one side last year and block and heads were both channeled so you might be pulling it out once you get the head off, fwiw, Smitty

So pulled both heads off and the right side was blown between every cylinder. The left was starting to go between every cylinder. I am sure the previous owner knew it had got hot at some point (just guessing) since it recently had a new sea pump and water pump installed before the sale. Lesson learned and it is used so it is what it is. Long block will be here tomorrow, mine was a good core. Will be putting it in first of next week .

Was that a MARINE long block. IT NEED"S TO BE.....
If not the cam will be too small and the clearances are too tight.