I reverse converted my old Ford pickup because the York compressor couldn't handle the added pressure. I did not simply evacuate and recharge, I replaced the filter drier, the compressor (because it was shot,) thoroughly flushed and put in mineral oil.
I would not reverse convert without flushing and putting in the correct amount of mineral oil. Although Ester is said to be compatible, that does not mean it can be the primary oil in an R12 system.
I hope I don't start an alternate refrigerant holy war, but I would NOT use ANY alternative refrigerant other than 134. They are either blends or flammable. Flammable refrigerant is used a lot but illegal. Blends have their problems because if a leak begins, the individual components of the blends leak off at different rates necessitating complete recharge to get it right.
As Steve Brotherton has often pointed out, R12 is the least expensive component of your a/c system. You will be much happier with R12 rather than saving $30 or $40 on a miracle cure.