iirc there was a board overview in the building manual, and also dimensions must be somewhere around?
hats off to your passionate enthusiasm, but i would suggest to build the mods as a prototype first before making a dedicated board from this, as sometimes things need to be tweaked or can be optimized, that is a pita on a finished board.
also adding the SIL jumpers is not really easy as some points are quite hard to access, and given their "far apart" spacing they will be very hard to solder into the right spot and are also prone to breaking. possibly it is easier to add them to the bottom layer and turn the board around. mind you also need quite a lot of space for the pots and jacks in the casing. the one i chose for my build is the minimum height for large TS jacks with pots on top.
and then there is the layouting, i think even with a two layer board you will have a hard time to route the signals to the pots (in a sensible order), and also you would have to be very careful not to run certain traces in parallel or too close to each other, it is quite easy to create a feedback loop if the wrong paths come together. (i also had to bend the wires in my build in some special order to minimize feedback whistling in the output, but it was possible to do)