While you had the IP out did you confirm that the governor weights were turning? was there resistance to turning the input shaft?
The only reason I can think of that would cause the advance pin to be sheared is because the IP seized, sometimes that shears off the shaft, I would think if that were the case the input shaft would now turn rather easily.
You obviously have more time than money, I would not go through all that work without installing a known good or rebuilt IP.
Do you have the factory port caps for the intake ports? if not be extremely careful not to get any trash in the intake ports.
Even with the fuel in shutdown and or the pistons (they actually are called plungers) stuck as long as the transfer pump is turning/working it should be pushing fuel out of the return port with the fitting (check valve) removed.
