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.
As others have already pointed out, that info has been readily available for many years. And it popped up easy-squeezy when I googled how much R134a in an R12 system.