My 2005 SXT RWD has single piston front calipers.

What do I need to bolt on the dual pistons? Not the huge BR9 cop brakes, but I think there was one in between, maybe R/T brakes? I'm ordering new front brakes and if there is anything that bolts on (unlike the BR9 which requires some machining) I'd rather order that!

 

BR9 wasn't an option on the Magnum anyway. All you need for the R/T spec two pots that year is the correct caliper bracket to mount the caliper and the rotor. Something else you can do is mount the police spec rear brakes for those years. Same caliper, larger rotor & different pads. Put both of those on your SXT and it will be a vast improvement.