On the manual, two thoughts: Some swear by the OEM which you purchase from Mercury. I like the Seloc better which is sold by Iboats, top of the page look under Boat Parts and Accessories. You can order online usage immediately....that's what I did and had an instant manual.
Top right problem sounds like low cooling. If the T stats are removed and the engine is run (as I recall.....disclamer) the block cannot fill fully and since the right bank is the higher of the two, that top cylinder gets over heated. Engine has a thermostat at the top of each bank and the pellet stamped 143F for the opening temp.
On a compression check, it could be as simple a carbon buildup causing the ring to stick to the piston and not expand on the compression stroke as it is supposed to to seal compression gasses. That loop charged engine uses pressure backed piston rings that expand on the compression cycle for a better seal since they only have 2 rings to reduce friction (I guess....maybe 2 is all you need with pressure backing). Anyway they have to be free in the piston grove to work properly. Carbon locks them in place and they can't seal properly and you loose compression. The hottest cylinder is a good place to suspect a problem like that which you are referring to in your questioning.
I'd put back what you undid and Google "decarb".....you can also find it herein in the archives. Perform that and run the engine for a few hours with a heavy dose of Sea Foam after the decarb....heavy dose would be 4 x the recommended maintenance mix of 1 oz per gallon of gas or premix, whichever you are running. WM and any auto parts store carries it. WM has it for 6 bucks and some change for the pint can.
After 10 or so hours of that, retake your compression numbers. Tell us what you get.
