There used to be Mercedes Engine Powered Thermo King Generator sets for the Refridgerated Trucks. They already have a Generator on them and a proper Governor and put out 220-240 Volts. In 1990 when I did that sort of work there were still some in daily use.
Might be easier just to find one.

The most of the Gen sets I have experience with ran at 1800 rpm when at full load.

There also may be a Marine liquid cooled.Exhaust Manifold for boating use. That would give you way more heat than the Radiator could put out and at cold temps that Engine may need to keeps the heat to itself.

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84 300D, 82 Volvo 244Gl Diesel