Pars, thanks for the offer, but if you haven't used KiCAD you're probably going to have at least as much trouble as I had.
Dr. Gilmore, Thanks you for the very generous offer. Here are jpgs of the schematic, bottom copper with and without the component layout, and top copper. I believe there is only one missing connection. My layout uses an aluminum bracket because the MOSFETs should be able to withstand 35 watts or so if the amp boards go south and the entire current has to run through the shunt. Most of the connections are on the bottom copper, with two vias to the top copper, and a couple ground connections on the top copper which could be replaced with a ground plane on top. This is my first attempt at laying out a PCB so if you find a better arrangement feel free to change it.
The 10M90S and DN2540 are available on Mouser, and I just checked that the 19NM50N MOSFETs are also available at Mouser, as is the SPX431. I chose those MOSFETs for their low on resistance, which is better than most, but other 500 volt rated MOSFETs can be used.
So the input electrolytic caps are 35 mm diameter.
The 0.1 uf/1000v caps (C3, C4 C9) are 27x11mm rectangular, 22.5 lead spacing
The 22 uf/450v caps (C7,C8) are D-Link 36.5x31.5 rectangular, 27.5mm lead spacing
C6 is 2.2 uf 50v
R12 and R18-22 are at least 1 watt, 500 volt, other resistors are 1/2 watt.