To clear the air:
racecars has developed a set of brackets and wheel spacers that let you put SRT calipers on an ABS (01-02) Gen 2 car. The master cylinder in the Gen 2 ABS car is the same as that in the SRT, and based on Dave's testing, the ABS controller of the Gen 2 works with the larger caliper volumes. Dave's target (applause, applause) was to get way under existing big-brake package costs. You purchase the SRT calipers and brake pads from Dodge, buy the brackets and spacers from Dave, and I think you're around $2500 when all done.
The 40mm rear caliper is for the non-ABS Gen 1 and Gen 2 cars. It's a simple swap of the OEM rears; no brackets, same rotors/pads/hoses, no cutting, same wheels, no offset issues, you still have a parking brake, etc. It is also a low-cost alternative at $630, yet based on brake performance testing (results are in another post), a very effective upgrade.
I can see it coming, a Viper brake-off. Everyone start thinking of the rules package.