You do not need to change your IVR when running a meter match. It has an internal regulator to power the fuel gauge. They say its only rated to run one gauge so you would need to use your existing IVR to power the temp gauge. So some modifications will be required to isolate the two.
You can buy those "calibration box"....its called a resistance decade box.
https://www.amazon.com/dp/B00023RTZO/?tag=fabo03-20
