You can buy or make your own Sanden compressor brackets. I found brackets for $70. I plan to use them when I switch over. I'm running a R4 on a 94 truck serpentine belt system. I just need one longer belt. If your evaporator is not leaking, just clean out the box and fan areas. The high pressure switch I was referring to is for a Sanden compressor. They only have a mechanical internal pressure switch. An electrical one is needed to shut off power to it. R4 compressors have a switch on the back side.
So, just replace your parts.
Here is a good write up for our trucks.