Check the stringers for rot
Replace the raw water pump. I would do a complete kit
Inspect the splines on all 3 pieces of the drive shaft
Keep an eye on the gear lube
could be a head gasket leak to the cooling water jacket that only leaks under load, could be the start of a manifold leak, could be the start of a head crack leak.
pressure test the cooling water jacket to be sure
from the mercruiser stickies
https://forums.iboats.com/threads/must-have-technical-information-for-diyers-an-work-safe-search-version-of.335378/
https://forums.iboats.com/threads/miscellaneous-mercruiser-information.323278/
and here are the videos...
No sticky
Swap heads, gain 30hp. Requires vortec intake
At 1150 hours, your motor should go another 3850 hours without an issue assuming you keep up with maintenance
Current ABYC requirements are the ladder must reach 32" below the water
Most companies offer 3 and 4 rung ladders
https://www.ggschmitt.com/retail-maintenance
Oil pan from a gen V is no where near going to fit a Mark IV block
You will need a Mark IV marine pan
I personally would look for a Gen VI motor to replace a gen V
