Gen3 viper rear calipers have 42/38 Pistons which happens to be the same as gen 1/2 fronts, as well as having the benefits of radial mounting. Gen 3 rears also shared the same size rotor as Gen 3 fronts at 14" x 1.260". Would it be feasible to use these rear calipers on the front of a mopar as they can usually be had for quite a few bucks less than gen 3 fronts? What difference would you feel using a 13 or 14" rotor with the 42/38 Pistons vs. the 44/40 pistons?

The hydraulics work out but you're going back to a much smaller brake pad. Are the pads the same size as the stock front pads?
The pads are what overheat and lose effectiveness in enthusiastic driving. Reducing their size won't be doing them any favors.

They use the same pad IIRC. I think Cass said you have to flip the transfer lines and bleeders because of how the rears are front mounted and the pistons are staggered.

They're the same size pads. Same calipers dimensionally, just with smaller pistons, and tubes / bleeders on opposite sides of the front gen 3 viper calipers.

I have a set in the rear, originally started with takeoff fronts in rear and front. I tried flipping the tubes and bleeders to match my original install, but gave up due to one tube thread being extra fussy. So just be aware- you'll need to run the rear-viper-calipers on the front side of the rotor in the front (if you want to bleed with them installed, anyway). Or you could pull them and stick a 1.25" aluminum block between the pads everytime you bleed them.