Not sure if this helps but my Coleman Powermate Generator makes 5000 watts with a 10hp Briggs engine, I know that a lot of the hot water skids with the 120 volt systems are 2000 watt generators like on a lot of the Landa systems, 5gpm at 3500psi (I have a couple of those) so I would think that as long as you have 2000 watts running whether it is AC volt or 12 volt, it should keep up with the burner unless I am wrong.
My 8gpm cold water rig makes 20 amps and when I bought it I was told that would be enough amps to run a hot box.
Not sure of what you are trying to do Greg, maybe just get a 2000 watt generator like the hot water skids use and rig up maybe a 5 or 6hp engine, might be easier to just buy a small 2000 watt generator.
Not sure how you would convert the AC voltage to DC for your purposes, that will be interesting to hear from someone here, I am sure someone like Russ J. knows or knows of another solution.