I have been playing with 69--72 Chevelles A/C units for many years. Just so you know. I get 38-40 degrees out of my center vent, Using a Temp. gauge from Advance.
If you are going to convert to R-134, Its a pay me now or pay me later.
A stock org. condenser will WORK very well "" IF "" you can maintain a speed of 35-40 M.P.H..... WHY? The stock cond. has tubes about 3/8" in dia., SO what. R-134 runs a lot hotter than R-12. ( It has a VERY different expansion rate, It runs about 20% HOTTER ) So, I would advise using a P.Flow cond.
The stock Org. A/C hoses.... R-134 will bleed through the stock hoses WHY?
R-134 has smaller molecules than R-12. I use R12/R-134 compatible hoses.
The Factory installed evaporator, Well chances are it is plugged up a bit, Wadda ya mean? Can you guess how many Cubic feet of air has gone through this unit in " 50 " years. ( I replaced my evaporator a while back.) WHY?
It was plugged shut around the edges and It was tough to see through. The new condenser, WOW, I could watch-T.V. through it!
The R-134 Charge. If you are working with a STOCK-C-60 unit converted to R-134. Use the 80% rule. 80% of 60 ozs. = 48ozs.
Charge your Factory converted C-60 unit with "" 48 ozs. "" of R-134 and DONT EVEN LOOK AT THE GAUGES. I drove my 70 to the Ohio show last week, The wife said turn on the A/C, FAN is on 4--- She says toooo kold turn it down, Now fan on 3--- She says toooo KOLd.... Fan is now on " 2 " it got a little chilly so I opened a wing window. Yes my factory (converted to R-134 operating well)
Also.......... If you can find a load of R-12 go that route, NOTHING is better than a factory unit with " R-12 " being pump through the system.
Yes, I said nothing is better than " R-12 ".