Confirm you adapted the larger original A/C compressor to fit on your Magnum swap? Post some pictures of the install please.
If you are switching over to R-134, you can swap to a serpentine belt drive and the much smaller and more efficient Sanderson compressor. If you already have a functional, original compressor and R-12, it would be better if you keep it intact to save the hard-to-get R-12. Then just unbolt the compressor and tie it up and out of the way.
Another thing to change if you are switching to R-134, is to install a larger multi-pass, parallel-flow condenser designed specifically for R-134 and always change the receiver dryer when the system is opened. Both parts are available at the link below.
