It's been 20 years since I last turned wrenches on or drove a Goat all of which brings back mixed memories.
Goats did not have power steering and a 3-53 would (from memory) have a big ole' valve cover sticking out the top. Also, the layout of the fan and accessories is not right for a Goat 3-53.
Try googling the PN or NSN off the data plate. You might find a "usable on" code that could be further searched to an end item LIN # or it's actual intended use.
The generator is a mModel DC 4.2. It's a 4.2kW, 150 Amp, 28 VDC genset. It has a starter/generator that can be used through the (two prong style) slave cable to either start the generator or provide 28 Volt power.
If you need the TM ,the number is:
TM 5-6115-596-14 Generator Set: Gasoline Engine Driven, 4.2 Kw, 150 AMP, 28 Volt, DC. Model DC 4.2 - Ord/28 (6115-00-857-1397)(20 June 1980)(Including Changes 1-3); 175 pages, 53 illus. [Operator, Organizational, Direct Support and General Support Maintenance Manual]
One place you could buy one is
http://www.military-info.com/mphoto/New1m05.htm
I've never done business with them but found them by Google
I've got a copy in the shop if you need some info right away.
We used to use these on M577 Command Post Carriers and kept one on an M151 in a fabricated bracket over the hood for slaving trucks and tracks in the motor pool. It can be stared by pull rope or slave receptacle. It will start from a truck with pretty flat batteries and then charge back the batteries pretty damn quick.
We used them to start M151s through M60A3s and M88A1s.
Quite a few of them were sold out of Chambersburg a few months back. They were all fresh from rebuilt stock and I'm kicking myself in the butt for not buying a few.
I don't know of any current diesel engined 28 VDC sets.
I found a couple on a hard target range in Germany, brought them back to the states (only the superchargers)and a friend is using them on top fuel bikes. Not that I am suggesting canabalizing it for such purposes, but thought it might be interesting.