Several companies make the brackets to mount a Sanden compressor in place of the RV2 you have there now. You will also need a temp control switch to cycle the compressor and the appropriate hoses to connect to the compressor. If you haven't already converted to 134a or similar you will also need to flush the entire system and replace hoses and o rings. It would be easier to just replace everything from the firewall forward as I did as the new style 2 pass condenser is more efficient. The challenger A/C system was never great at making cool air even with R12 so don't expect a miracle.