Replacement brake pads after upgrade

What is a "Stage 1"?

If it is a OEM based system, there are two types of calipers/pads that used 10.98" rotors. In turn, they had different mounting brackets.
One is the E-Body type, which installs with two long pins. The tabs on the pads have a hole in them. Several aftermarket brands of pads include "39" in the part number.
The other type is the kind used on the '73 and newer A-Bodies. This is the slider type, and uses screwed in tabs on the caliper bracket to attach the pads. This pad often has "84" in the part number.
As noted by Pishta, both of these types of calipers/pads/brackets were used on other types of Chryslers. As far as I know however, the slider type was never used on E-Bodies, and the pin type was never used on A-bodies. That could help you when buying pads.