Can you prudently convert a R134 compressor to accept R12?

A used engine I'm placing in my 1988 300TE which uses R12, came with an A/C compressor for R134.

I do NOT want to convert my system to R134.

Please advise,

Thanks,

Neil

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.