nikkidanjo and Jason did a write-up on how to convert the gauge to be linear and respond to the 0-80 PSI 10-180 ohm sender (I think its 10-180 anyway).
The issue that comes up is the gauge is very dampened. Some people claim to have success using a sonic cleaner (the ones used for cleaning jewlery) with acetone or 91% alcohol.
That method did not work for me.
Another method suggested is to get a compressed air tank, soak it in the acetone, then put the needle back on the gauge and use the compressed air to spin the needle at high speeds. That works temporarly, but it did not seem to remove the grease from the gauge entirely.
I was able to remove the dampening fluid by "drilling" a hole in the back of the gauge (there is a little white nipple that stops the needle from dropping off track), and soaking it in the acetone. You ahve to be careful because if you drill the hole too big and the needle no longer rests on it, then the needle won't move at all (although if you can fabricate a new stop to it, it will work, this is what I did with my first gauge).
I was planning to do a write-up for this, but never got around to it.
Lastly, Nikkidanjo did the rewind gauge mod which linearized the gauge by adjusting the winded gauge wires. Thats a bit more involved than I like, but you can find it on google very easily.