Bring temps down to approx. 40 to 42 deg. I have been doing this proceedure for 2 years with no reprocussions. Any questions, e-mail me. No, it is not worth it.
Car is too old.
I would suggest 407a as it has closer values to R12. They both are compatable with r12 oils and an oil change is not required. High side pressure will also be slightly higher. Take your temp at center vents. Bring temps down to approx.