I can't answer your question, but why do you think you need to "upgrade" the rear calipers? How do you use the car... do you run it in track events?

My '88 190E 2.6 is 57% front heavy. In a maximum performance stop of about 0.9g it goes to 70 percent, so the rear brakes don't have much work to do.

I've run it in track events a couple of times. The first was at Firebird Raceway as part of the '92 Starfest event. The brakes were fine even though by then I had swapped out the heavy dusting OE pads for low dusting Repco Deluxe pads that required higher pedal effort, but they didn't exhibit any significant fade.

A couple of years later I ran an event at the big Willow Springs track. Again, no problems with the brakes, but on that higher speed track the suspension was too soft with insufficient damping to control body motion. It just kind of wallowed around in the long 80 MPH Turn 2 and 100+ MPH Turn 8, and I have never run it in a track event since.

Duke