Most sportfish motors are permanent installs. The blocks will never leave the boat without tearing the entire floor out of the cabin or cutting a hole in the side of the hull.
These installs usually have a fairly wide span between the center stringers, and for a good reason - they lay plywood runners on the hull bottom and use little carts with wheels on them to "freight train" the heavy parts in and out. Luckily, sportfish boats let you remove enough of the rear floor to be able to get the pieces rearward where you can hoist them out. Aft-cabin boats must have the pieces "carried out by hand" or plywood traintracks laid all across the living areas.
One good thing is, that most huge diesels split the pieces up into manageable chunks. The MTU you speak of, I believe, has the cylinder heads in 2-cylinder sections (six 2-jug sections in all). The heaviest and most cumbersome piece that will need to be handled is the crankshaft itself (and believe me, it is a bad mother). The cylinder liners are all removeable. You "should" have enough room to get the crank out from under the motor without taking the block off its mounts, but each install is different (this is why a lot of big diesels seem to have a lot of room under them). Drop the pan, pull the rod caps, take the pistons, rods, and liners out from the top as an assembly. Pull most of the main caps, jack up against the crank, pull the remaining caps - "unjack" it into a wood cradle or blankets. Drag her out.
Best I can remember, a bud's 1150 Cat TOP-END job was $45k. To add the bottom-end to the job was another $15k. Brand new (or much newer tech factory rebuild - can't remember which) motor was $60k. Didn't matter, though, cause there was no way to "SWAP" the old motor out and get the new motor in.
A broken rod and damaged block will kill the deal in a heartbeat!
The source of the "sieze" needs to be determined.
Furthermore, it needs to be determined what CAUSED it to seize. If it is/was an oil starvation problem, it may be a goner anyhow...
Aint that great news?