I also have a 5411 & the real question to ask yourself is
if that engine is likely 30 years old, what if any parts are on it that you will need, or will even be feasible to re-use, other then the block?
Most of the parts on that 5411 will be in the same state of corrosion as your 5411 motor. The most common parts that fail on the 5411 & all diesels are the exhaust elbow corroding & blocking, the fuel injection pump failing, the impeller failing at the water pump, the pump leaking at the bearings or oil filler cup corroding away, the glow plug assembly failing, rusted out oil pan, the starter, etc. If you do actually manage to get any of these parts off the old motor without damaging them (not easy as all the bolts are frozen on from rust corrosion) then how long will they last before they also need replacement? In my opinion, I would not waste a thousand buying a bunch of used parts. Now if U can get him down to $500. then it may be worth it. Come to think of it, a new starter is $400 or more, & if it has a Hitachi alternator then its worth $750. new. But those are new prices. Personally I wouldn't want to spend the money, just to find that the parts were corroded past their worth. Plus when I replace a part on my boat, I always use new parts, so that I don't have to fix it again in a year's time. Remember that this 5411 has as much wear, & likely more then your engine does. Our 5411 don't have the greatest rep. for creating enough oomph in the power dept., but they are damned reliable.