I would guess (never been there myself) that you should start with an oil change, check all hose
lines leading to engine and tank for bad or missing connections, change out the filters if you have any, and drain the Racal water traps if these are in place, bleed all introduced air out of gas
lines afterwards, check the starting battery for power and wiring to starter for good electrical continuity, check condition of belts, check condition of impeller and replace if questionable, check condition of throughhull and intake of cooling seawater including filter making sure it is clean and flowing to impeller, examine
exhaust path as best you can for rust and corrosion, manually crank it over, check
fuel in tanks and in filters for proper color, try to sample
fuel from bottom of tanks, then turn the key and see what happens. Somewhere in the midst of this checking activity, I would recommend that you also locate a near by source of good diesel mechanic skills and engage they in some practical "what if" questioning. If all these check out chances are you will have compression, and power to the starter motor. So if the starter turns it over, and the
fuel is present,with air properly bled out of
fuel lines, it should fire up. Contaminated
fuel is probably your main risk. If it starts to run, immediately check for sea water flow out the
exhaust pipe (should be there) and examine
exhaust smoke if present for color, and check for smoothness of engine running, watch oil pressure gauge for proper reading, shut down promply if anything seems suspicious. You know how to cut the
fuel source right ?