You left out a few particulars about the engine and your own situation.

First off these Volvos are raw water cooled. If this is a salt water
vessel, it is probably nearing the end of its useful life due to corrosion
of the cylinder jackets and certainly of the exhaust manifold.

Parts for these engines are very expensive. The exhaust manifold is $550
last I checked. A piston is $500. I was never brave enough to price out a
cylinder jacket. The good news is that if you have the time and
inclination, you can build up a boneyard of used engines for about
$200/engine. The MD11C is parts interchangeable with the MD-2 (provided
they have the same injector style). The bottom ends on these engines are
built like a tank, so it is normally only the top end parts that contain
cooling water where you must be concerned. All top end parts are field
replaceable without pulling the engine.

An engine survey will be very expensive and inconclusive. I would suggest
that you have a competant marine surveyor survey the engine at the same
time as the rest of the boat to make sure that there are no major problems
(water in the oil, water in the trani, unbalanced exhaust temps., poor
starting characteristics, sooty exhaust, etc.). Then negotiate the
purchase of the vessel as if the engine were completely shot and needing
replacement. That way if you do have to repower, you are protected and if
you can limp it along, you are money ahead.

You didn't mention your mechanical expertise. If you are expecting that
someone else will be doing your mechanical work for you. You will be money
ahead to repower with a Yanmar (probably about $8000 installed)

An engine survey? What does the engine surveyor do for an old diesel
engine?

Are you, the reader , familiar with the Volvo MD-2 diesel? What's up
with

em? Can the run and run and run?