Maddog:
You might try looking up your model under Fastlane and comparing the parts numbers to find similarities. For Example:

87 300E 70340 booster/33750 master cyl./1040 102348 rt frnt caliper
92 300CE 70340 booster/33750 master cyl./1040 90178 rt frnt caliper
92 400E 59102 booster/12251 master cyl./1040 90178 rt frnt caliper

Comparing the above shows that the 300E (single piston caliper) and the 300CE (dual piston caliper) share the same booster and master cylinder part number. The 300CE and the 400E share the same caliper part number. This indicated that the 300E booster and master cylinder will be fine for the 400E caliper, as that is what is done on the coupe. This would seem to make sense as the 400E is heavier, especially up front, and probably needs the additional boost. Being lighter, the 300E doesn't need the boost/master cylinder change, which might result in overboosted brakes.

__________________
John

2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)

Click to see 87 300E