ac evaporator

No real problem if the AC compressor is over-sized since it is cycled on & off as needed. I put a Sanden "shorty" H13 (13 being displacement in cc?) in my 1985 M-B and cools fine. I understand there is an even smaller H12, but most brackets are made for the H15 length Sanden. If your evaporator becomes the "limiting factory", it should still work great, since the factory AC in my 69 Dart was icy cold in FL (using R-12).

Re refrigerants, I run Duracool (hydrocarbon) in all my cars now. I changed the 1996 & 2002 ones to it recently when both compressors seized. No sense going back to R-134A since it is to be banned (already in France). HC is used in home refrigerators in Europe. Read for yourself and try to weigh the rants from AC professionals. I use PAO 68 oil, which seems best for any refrigerant.

I recently searched HO-1234yf and read that M-B did simulated crash tests which found a puncture burns violently (from oil spray), which converted the refrigerant to deadly HF gas. It etched the windshield and is very bad for your corneas and skin. They refused to use it and are currently fighting France over denying import of their cars w/ R-134A. Might be over-blown since Freon changes to deadly phosgene gas in a fire, but we used it for decades. I fear not the 12 oz of Duracool in my cars. The cans feel almost empty.