Here's a link to some pressures you should be seeing:
http://www.ackits.com/aacf/ptchart.cfm
At 90F, you should be seeing 190-230 on the high side, which you seem to be getting. The low side, they say, is about 22 psi.
When you noted your numbers was this at idle or at higher rpm like 1500 rpms?
When I charged up my 420SEL (R12) I tripped the auxiliary fan, and disconnected the idle control system so that the car idled at 1500 rpms, then met the numbers in the chart appropriate for my ambient temp. You might want to try that..
W201's center vents are directly attached to the evaporator you should be getting rather low numbers from them compared to a w126. My 190E, last time I checked, gave me high 30's when it was high 70, low 80s outside. I don't have R12, but rather ES-12A.