Ok, finally got a real in dash guage for myself. Put the new sending unit on ($20) and tore into the instrument panel. There are 2 resistors on the back, big (physical size) too. One is on the top, one is on the bottom. If you look on the circuit sheet to the right and lower, you will see a resistance for each one, top being 20 ohm, the bottom being either 520 or 540 ohm, I can't recall which. Ayhow, you need the top one. I just took it out and soldered a new wire in it's place. The hardest part is just getting the speedo cable out, for me at least. If I had some pipe cleaner arms, it would be a lot easier.
New guage reads N at idle, R at 2000+ RPMs
-Ben