That pump will fit, but as racerone says pull your apart and check the diaphragm.
OEM diaphragm is F438747 and gasket 820490 (F438760)
Sierra aftermarket kit which includes some other gaskets too is 18-7806-1.
BTW: I see you have the DELTA CD box and the ignition coil is not the OEM. My question is as that CD box has three wires and the coil has three terminals +, - and GND. The other CD boxes (Motorola brand) that was used had only two wires. Do you have all three wires connected and how to the coil? I have that CD box as spare but have not figure out if it is okey or not, or if the coil is bad. The CD box is giving a "Hmmmming" sound (as by the book) when power it and that is right it shall, but I do not get any spark. Maybe the coil is bad but coils with three terminals are uncommon.