Are you converting because it doesn’t work any longer, or are you converting because you want the new safe freon gas to save the environment?
Either way, you should call a commercial refrigeration repair man… There ia a new drop in replacement called “Hot Shot” R414B refrigerant. A blend which is recognized as non ozone depleting.
Originally developed for automotive use, it is now widely used as a drop in replacement for R-12 in commercial refrigeration.
If you use R414B Hot Shot, you will not have to change the oil from Alkyl- Benzene, to Mineral oil , or Poly_ol Ester… Look it up on the web.
Again I say that this is a drop in replacement.
In my humble opinion…!