Howdy,
I would suggest you look at all the factors of the unknown.
1. if batteries are present, trickle change them fully. If not, buy new batteries and charge them before use.
2. look over all lines, fuel, fuel return, wiring etc..
3. open air filter and at least blow out, maybe replace if needed
4. fuel - I would drain any and all fuel. replace 2 fuel filters
5. oil - I would not spare the expense of oil and new filter. I long drained my unit and put high quality oil in and a new filter.
RTFM - understand start-up procedure of your unit, understand what a run-away diesel motor is and how to shut it down.
*understand what the starting sequence is, manual crank in normal position, turn switch to prime and run, listen to fuel system and fuel pressure building, turn to start and hold there a moment until you see oil pressure rise on gauge, release switch.
Turn engine speed adjustment to bring inline to 60Hz, turn voltage adjustment to bring to 120/240 (single phase)
Have equipment ready to test. Amp meter to check your voltage and frequency. To double check your gauges are operating correctly on the panel too. Simple things at first for the convenience outlet such as a light. Remember that the breaker for the convenience outlet is the GFI test and reset, and inside the panel the 10amp rocker breaker.
I would also suggest you have proper wire to the lugs and put some good loads on your unit. I found my unit to have started to wet-stack in its prior life. A good hard load of 100% for at least a hour will help clear that up. I actually removed my exhaust manifold and pressure washed it, and used a screwdriver and knife to clean out the ports on the head.
Good luck with your unit. Report back with your results.