One Thirty Four A will not get as cold! In my R12 cars I get 34 degrees at the vent. With the 134a maybe 48 degrees. Major benefit in favor of 134a is it cost $4 to $5 a pound as opposed to $30 to $50 in the case of R12 if you need a recharge. Find the V-Kool Dealer in your area to put on the invisible window tint to drop the heat load and be $$ ahead with R134a.

In all fairness I am a V-Kool Dealer in Kansas City ( 4th largest in the nation ) but spent 20 years in the HVAC business and still keep my license. We do not do cars here, only residential and commercial.

In many major markets there are automotive ( curved glass ) dealers. I do have it on all of the windows ( including the windshield ) of my Axiom and it passes the stringent Missouri inspection because it is simply invisible while blocking 55% of the heat through the glass.
I love my "new 1984 380 SL."
Best Wishes,
John,
Licensed HVAC Master Mechanic