By the OP's lead-in, I assumed the in boat work would be the tech's issue... and the fact that it's a single vs twin, there is room to work (and retrieve from bilge).

Personally, on a stand is preferred but when you are paying a marina by the hour, the bill goes up fast - and this is still an inspection to determine the failure. Also, until deposit and assembly starts, chances are "pulling the engine and putting on the stand" will actually be sitting the shop floor where parts mysteriously go missing. My $0.02

Not true put motors next to each other on stand start transfer & replace best way! It's not easy plugs wires while in boat under motor unseen damage etc etc good luck! Also try 1800runsnew new or rebuilt 454 mag bullet proof 10+years or more my 02

Thanks guys. It's a single with lots of room with a large hatch so lots of room for a boat. Like I said boat runs. Was running WOT at 5100rpm prior. Then one day it starting running weird after 4400rpm. Props are fine for this situation.

Compression numbers were consistently 130-140

Once again the boat runs, pips up on plane, does mid 40s, just wont do high 50s and I get water kn starboard cylinders when shut down and then wont start.