Need generator specification

One could GUESS the output spec based on just the engine's horsepower, but that wouldn't be accurate without understanding the variables of circumstances.

First off, it's a diesel engine, but is it burning DIESEL fuel?  in stationary applications, it's equally common for the engine to be fueled by natural gas, in which case, it will be making significantly LESS power, and the generator unit will be derated for that circumstance.

Will it be operating at high altitude?  Generator sets are frequently identified with derating for higher altitude not just for thin-air horsepower reasons, but for thin air thermal-transfer of the generator windings and prime mover cooling system.

Generators made for low-altitude, foliage/swampy environments, will be insulated with special materials to reject fungus... the loss in thermal transfer as a result of those coatings will effectively reduce the cooling rate, thus, requiring a derate.

Finally, synchronous speed.  The engine may be capable of churning out 120hp at 2300rpm, when coupled directly to a 60-cycle synchronous generator, the shaft speed for the generator will NEVER be 2300... it would be 1800rpm for a 4-pole generator, or 1200rpm for a 6-pole, which means the engine's horsepower curve would be in some other realm... so a reduce in output as a result of that.

Nutshell answer, the generator's output is never MORE than the prime mover's output, it's usually substantially LESS.

When serious generator units are put into service, the output specs are usually identified in 'as-built' documentation based on all the aforementioned characteristics, AND others... and as part of commissioning, the unit is proof-tested before contract acceptance.

Lacking the machine's documentation, the best answer will be to look on the data tag inside the unit... as that's where the commissioned and proof-tested output will be identified.  IF you're very lucky, you'll open up one of the panels to find a copy of the documentation set inside a sealed metal compartment...

And I see you've clarified your question, narrowed it to weight.

Again, it's provisioning, you wouldn't find anything other than a 'range', because it depends on how it was fitted up.  All we could do, is 'wild guess'.  It'll be more than 3000, but probably less than 7000.

No piston squirters on the underside cooling the piston crown. These usually are straight from an oil gallery internal to the cylinder block from the oil pump.