I realized that the above description was a little vague so I made a special trip to get the sender. I would like someone with a spare sending unit to compare the following pics to what they have in order to determine what years, if any, have this style of rheostat assembly mounting. With this information, I can find one on a junk yard unless what you have is for sale.
this is the rheostat assembly as it appears on the complete sending unit. Take note of the white plastic piece which locks the rheostat onto the steel lines. With this removed, the rheostat simply slides downward and off of it'* mounting perch.
This is the rheostat assembly removed from the sending unit
And finally the connector
I need to find one that has an operating range of 0 ohms empty and 90 ohms full. I believe 97 was the first model year that began the 40/250 range but I'm not positive. If you happen to have a multimeter kickin' around too, you'd be my hero if you could measure the range.