TwoDoor, in his thread about his gas gauge gives me hope. I need to do the same on my 50 coupe and have pulled the plate off the firewall but going to need smaller hands to get in there! I did not want to hijack his thread as it didn't specifically answer my question which is......

Doesn't the gas gauge get its power from a wire from the switch?...and if it does, wouldn't the Runtz work as well, located close to the switch, since its still close to the guage? I have the Runtz and need to put it in but like TwoDoor said, its not easy, for big guys like me, to "get over in there" and while I have done other gauges they were a lot easier for me to get to...thus the question!
Comments on my question welcomed

I would think that would work, since it's wired in a series, it really shouldn't matter where it goes. I would make sure it is mounted so it doesn't short out and that it is grounded.
As an after thought, I didn't check on mine to see if it was like a diode that allowed current flow in only one direction. That may be something you want to check. Good luck.