Walthers used to list a Prime Mover locomotive engine. Sorry I don’t have a catalog at hand to check the numbers for you. You could go to their website or check a catalog to see if it is still available.
looks like it might be easy to fabricate an eight and/or twelve cylinder version out of styrene with or without the generator using the walthers model as an example. that is if you are particular, doubtful that very many people would notice the difference, though.