Just swap out...
The compressor from your removed engine to the new engine. Since the system is already evacuated and disconnected, you should be able to swap out the compressor while the engine is on the stand, then drop it in and make the connections. Since the system had been exposed to the atmosphere, you should replace the receiver/dryer as well. Once done, vacuum check for leaks and recharge with R-12.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.