The remarks about R134 not work as well in an R12 system are correct. However, there are ways to help it out. It doesn't.. without getting to engineer, carry the heat as well. (its enthalpy doesn't change as greatly with pressure as does R12) Running the higher pressures helps with this. I haven't tried this on the yota, but when the condenser went, my dad put a new condenser core from a newer model benz on his old 79 years back. When the evaporator core went, he again sought a larger one from a newer car. With some epoxy and plastic it was stuffed under the dash. The result was AC that functioned so close to original you couldn't tell.

Other things that help are finding ways to keep the air moving past the core when sitting still. Wiring up an electric fan for example is one way. If you have one, wire its realy in parallel with the temp sensor so it comes on with the AC compressor. That's probably getting deeper than most people to go but it's all about the heat transfer and moving more air through the core helps.

Frank