I stand by double. You may find a fly by night shop to remove, rebuild and reinstall a marine engine for 5 to 7 grand each, but a real and competent shop will be considerably more.

This is a situation where you will get what you pay for and the value will be in a quality job as apposed to front end savings

Thanks for the input and info guys.. SJ

I'm not sure about any pricing because I do all of my own work, but I will say that it seems that a lot of people think that engines are done at the 400-500 hour mark.

Head work "could" be required, but that may be more to do with corrosion than anything else. Merc's blue motors need top end work at predetermined hours because of the stresses put on the valve springs, but that's about it.

I went through my 454 Mag because I found that there was a questionable piston in hole number two (I was adding a blower and didn't want to risk anything... had I not added the blower, I would have let it be). Outside of that piston issue, the rest of the engine was pristine, and that was with 400+ hours (the thing looked brand new inside). Let me add that the heads were changed before I bought the boat, but the issue was from a corrosion failure.

With the above said...(you didn't mention hours or condition)... If the engines are reliable and running well, and not using oil outside of specs, then I'd leave them alone.

Parasail boats I ran we had 330hp 454s with 4000 hours on them running like a champ.

Saltwater motors , put new risers on after a 2nd year, new manifolds and risers year 3 , and after year 4 new motor.
Motors still ran great , just beyond their useful life.

Ran them pretty hard too. Not wide open all the time but 4000 rpms could be pretty common.

Had a PTO running off the front of the motor pulling 30 - 40 horse engaging and disengaging 1000s of times over also.