I feel your pain. Boracay came with a Ford 2702E slant 6 engine
of 3.54 litres. It was hard to start and poured out oil
. The 40 litre drum of old engine oil on the boat should have been a clue.
After more than a few boat bucks on "repairs" and a few opinions that "those Fords are great repairable engines"
I bit the bullet and installed a John Deere 4045DFM/ZF63 gearbox
. It turned out to be heavier than the 2702E, but has been very reliable since.
If your engine/gearbox is in generally good condition then repairing is worth considering. Looking at my old installation
the engine would have had to have been lifted up in the boat so it would not have been a "$25" job.
Do keep in mind that these are now around 50 years old, so manuals
could be scarcer than hens' teeth.
You mention having a 2701 engine which would be the 4 cylinder version. If so the Yanmar
could be a good replacement.
However if you have a heavier boat (Boracay is about 15 tonne) then a bigger engine may be indicated.
Some members with turbocharged engines have not been entirely happy...