I have been struggling with this for a few months, trying to find a correct 80 psi sending unit. Your gauges will not read correct with a 100 psi unit. I'm sure there is some sort of conversion you could do mathematically to calculate the actual reading of the gauge, but that's beyond me.

I was thinking something like this - 100/80 = 1.25. At 60psi divide by 1.25 = 48 psi. So, your 80 psi calibrated gauges with a 100 psi unit reading 60 psi, is actually 48 psi due to the calibration difference. Again, I'm not sure my math is right.