Need help diagnosing really weak rebuilt 350

Long story short, I bought a long block for my 20 ft boat. Put it in and it was very weak. It was supposed to be around 275 hp, but obviously wasn't.
I did a compression test with it still in the boat, and got very poor compression numbers. I then pulled it out and checked to see if the cam timing was on, at the engine builders recommendation. It was. I then did a leakdown test and these are the results I would like help interpreting.

cyl 1 - 11%, just a tiny bit past the exhaust valve, the rest past the rings
cyl 2 - 15%, a little past the exhaust valve, the rest past the rings
cyl 3 - 25%, a lot past the exhaust valve, the rest past the rings
cyl 4 - 18%, a little past the exhaust valve, the rest past the rings
cyl 5 - 23%, a lot past the exhaust valve, the rest past the rings
cyl 6 - 26%, a lot past the exhaust valve, the rest past the rings
cyl 7 - 15%, a little past the exhaust valve, the rest past the rings
cyl 8 - 11 %, a little past the exhaust valve, the rest past the rings

I could not find any leakage past intake valves on any cylinder, but every single exhaust valve was leaking, some pretty bad.
My main questions is this:
Is ANY leakage permissible past the exhaust valves?


Thanks