I dont mean to crap in your shoe polish but if you define the circumstances, and YOUR meaning of the word 'pump' you will get a more definitive answer!
Short story - the 99 pump will work in a 96 pump/ sender assy.
The 99 assembly will not work in a 96 tank.

So yeah.. we used too many words to say the same thing. Good to know you figured it out, would be nicer to know how.. but whatever.

 

Went and bought a pump assembly. Turns out whoever owned the thing before we did put a pump in and butched everything up. One of the ground wires on the harness for the pump was broke in half, so they just ran a hot wire to the fuse box and ran a new ground.