stalling with AC on, coming off of idle

In hindsight, it was a lot of Freon. However, in my defense, the available information on how much 134a to use in a conversion from R-12 is not readily available.
That is not correct. If the system has all original components (no non original parts such as an updated condenser) the r-134a charge should be about 80 % of the R-12 charge.