Thanks for the post Scott,

You are correct, the original pump is obsolete.

If you're going to rebuild it you'll need to make sure the Crank, Rods and Pistons (and Rings) are all in good shape on your original pump, as these parts are no longer available.
If it's not knocking or if you don't have obvious damage to these parts, then it's worth it certainly. You can install new Reed Valves and Gaskets in the pump for around $50 in parts.

Conversely, you could install a similar pump but there would be modifications necessary, such as changing the motor Pulley (as your pulley is a J-6 poly-groove pulley, unlike other pumps which have a v-belt) and drilling holes to mount the Pump on the base plate.
It really depends on the condition of the pump components.

- MTR