You could also use an A500k pot but wired in reverse (swap 1 & 3) to get the same taper as C but the control will be backwards from the way it was intended. I do this all the time with rate controls on LFO's....
Because it takes 20 seconds and they do get in the way on tight builds like 1590A where there is no room (usually) for a battery anyways. Also the chance of soldering to the wrong tab is reduced to just about 0 because of the slanted side locating the sleeve tab.
Just thought I would chime in about something I saw in one of your pictures. It's around the charge pump IC, the electrolytic caps look bulging to me although it could be an optical illusion from the angle but if they are roasted might try replacing them with a higher voltage rating. Again, I...