I have reverse converted a number of systems with great success. The procedure is documented in numerous threads on this forum, but I will repeat it once again:

o If the system is not empty, recover the remaining 134.
o If there was a leak that led to service, repair the leak.
o Break all connections and flush all lines and components thoroughly preferably using a/c flushing agent, but Brake Cleaner or Mineral Spirits will get the job done. Blow the flushing agent through the line and then blow all of the flushing agent out of the line or component THOROUGHLY with compressed air.
o Remove the compressor and turn it by hand to empty as much oil as possible. DO NOT flush the compressor with flushing agent, use Mineral Oil for this purpose.
o Distribute the correct amount of Mineral Oil through the system by pouring a little in each component.
o Put the compressor back in place, turn it by hand at least a dozen turns to ensure that it is not liquid locked with oil.
o Lastly install a new r/d and don't do it until you are ready to immediately begin evacuation as soon as it is installed.
o Evacuate and charge the system with R12.