Dear Jmardy,
I have owned two Panteras for over thirty years. One still has the York compressor AC system. The other one was converted to R134 in 1998.
The old stock AC system has soldiered on over the decades. It cools as well as a Pantera can and is comfortable. It has even tolerated various iterations of engine power and rpms without problems.
The R134 system has been a headache since 1998. I finally took it to a qualified Pantera mechanic in DFW with lots of experience with heat, humidity and Pantera AC problems last year. My issues had nothing to do with the R134 swap per se, but rather the covert combination of two or three electrical connection issues that cascaded into badly problematic function. It *finally* works properly.
You can make either R12-stock or converted R134 AC systems work well with enough time, money and attention to unsuspected details (electrical connection high resistance, etc).
I would suggest that the current Craig's List and eBay price for actual R12 Freon around here is $35/pound two years ago. If your current AC is working properly and you have some other "items" on your Pantera performance punch list, then the most pragmatic course would be to simply buy a modest supply of R12 and postpone conversion to R134 until the invisible hand of economics nudges you.....
Warmest regards, Chuck Engles