Industrial 12A is completely compatible with 134a. IT Is not R12, don't confuse the two.
Also you are not mixing anything as long as you stick with pag oil. as you need to completely evacuate the system. The only thing left is the oil. I vacuumed mine for two hours and leak tested it. No I definitely would not put R12 in, but normally you can use R12a which is what Joe Kincaid who makes these unit uses. I evacuated my car again and tried 134a. It seems to be working well so far, played with the volume a couple times and 2 pounds 9 oz seems correct. Give or take a couple of oz.
My sugestion is to only use 134a because I believe the orfice in the txv freezes up.
Need to drive it more to confirm it is working well.
Barry