Well, this project is over. I found a NOS HO MJ p/n 4637184 fuel sending unit buried in the archives of Ebay, send the guy an email, and he still had it, $55 shipped. In comparing the XJ and MJ HO units, I suppose the XJ unit could be modified, but it would take a lot of creativity. About the only common part is the potentiometer itself and float. But it's real easy to change the sender's output voltage polarity and use it in a Renix application. Both ends of the pot have solder terminals. Simply remove the BLU wire and resolder it to the other leg of the pot and the voltage output polarity to the gauge is reversed. Tested and verified. :D I do not have a Renix sender but I'm sure this will work as well providing both ends of the pot are accessible.