No, you need to multiply the R12 capacity spec by 0.75 to get the correct amount of R134a. Nonstandard components can throw off this calculation—a new filter-dryer that's a different size than the original, for example, or a parallel-flow condenser instead of the original serpentine type so the system has a prayer of doing a good job for you.
Put a meat thermometer in the AC duct Keep adding 134 freon until the duct temp gets to 55 - 50° then the system will be full. Should be close to the same amount of freon in the specs.
Lookit-a-thermometer is fine for a quick, general evaluation of A/C system performance, but 50° isn't some universal magic number; the temperature you want to see varies depending on ambient temperature and other variables.
You charge an A/C system by weight, not by guessing based on what a thermometer says. Also, there are no meat thermometers that read anywhere near low enough for this job. Second preference is to charge the system by reference to the manifold gauge readings—but you have to know how to intepret them, and these readings also vary with ambient temperature and other prevailing conditions, so you also have to know what you're doing.
A/C work by guess and by gosh is a pretty dependable way of breaking stuff and wasting money and endangering yourself and ending up still sweating. It's better to do it right.