How lucky do you feel?
The engines are the huge gamble and you will not be able to judge what your getting without a bunch 10-50 hours of operation.
The hassle is diesels are basically wide open to a breeze and moisture so rust of the cylinders is the danger.
A diesel can be land started with a hose to provide coolant on the sea water side , but the engine with no load is suffering from cold operation , which will blow acid into the oil.
The proper technique was of course to pickle the engine , a tedious process but an engine can survive a decade or two of storage when done right .
If the boat is worth the effort price wise I would launch it start it for 10 min and change the oil and filters.
I would then demand about 20 hours of moderate to heavy loaded operation and call the engine guy to do a blowdown test.
However if it smokes white when warmed up , after 20 hours , just tell the engine guy to bring an inframe kit (if an industrial block) or an engine or two if a throwaway like a Cat 3208.
Good luck,