Thank you all for the valuable input.
I have made the conversion to R134 and it's working for now. If anything goes wrong I keep a spare Accumulator/Compressor as backup.
Interesting thing with the A/C bypass on the 3.8 TS. Unfortunately mine still has engine oil pressure issues (changed Oil Pressure sensor so far), if we'll figure that out then maybe we'll start putting some money into it if it's worth it (engine ok).