That makes sense, but the power is much reduced at 1800. for 30kw you would need at a minimum 30kw/746 = ~40 hp, which sounds reasonable. Probably need at least 60hp to cover surges and generator efficiency.
You don't HAVE to turn the generator at crank speed. (Belt drive or gearbox) Bear in mind though, that old style, synchronous generators are VERY inefficient. One source I found suggested less than 20%
But most 6's / truck engines are very torky devices, and generate most their "oomph" at fairly low RPM. I would think a typical slant would be "right at home" at 1800
I mentioned Onan twins earlier. These are common in motorhomes and run typically at 1800, much much quieter "out of the gate"
