Worth consideration..
Nostalgic AC - Binary Switch w/ R-134a Discharge Port 7/16" - AC Pressure Switch - Oil, System Flush & Switches
But I would suggest tossing the included pressure switch, 398 PSI compressor cut-off is definitely a bit high for our ancient systems, especially if you keep the non-barrier hoses (recommended).
I recommend a Red Dot 71R7500, much safer, more conservative, 325 PSI compressor cut-off. Also has the 3rd element for controlling fans or louvers if the conversion to R-134a forces you to go that route.
Amazon.com: Red Dot Trinary Pressure Switch - Generation II 71R7500: Automotive