correct me if I'm wrong sweeper, but you've got a temperature of 4.1C after the bulb? That's not the same as a superheat, unless you're using a T1-T2 function on the TC reader (doesn't look like it based on the LCD). Based on your gauge reading, I'd say you still have 20~30C superheat. You should keep adding charge until you get subcooling (got a sight glass?)

Your compressor will be hard to start with R507 because it's an R134a compressor AJA2419YXA. Y=R134a code, Z=R507 code

R134a uses a lot more compressor displacement per motor power than R507 does. In the case of that compressor, Tecumseh makes the same compressor for R507 AJA2419ZXA, and my guess is it has the same compressor parts with a (more powerful) motor more suited to R507.