I have an M50 in an E34 and just did the ac this past weekend. You SHOULD have two ports close to one another right along the inner fender. High side being the large port on the small line, and low being the small port on the large line w/insulation on it. You've replaced the TXV expansion valve, receiver dryer, and compressor. How about your evap and condenser? Has this system ever had stop leak, or "seal enhancer" pumped into it? If so that garbage solidifies in air and can totally plug the heat exchangers, lines, basically it can destroy your ac system. What your describing is either a retrofitted system with the low side fill adapter placed on the high side r12 port (hence the readings) and may be missing the other adapter hence why you can't locate it. OR you have a completely plugged system, (which wouldn't make much sense since the pressure increased on what SHOULD have been the compressor suction side). Double check it all for kinks in the lines, if it's all good make sure you are in fact on the right side (low side) vapor charge it after pulling vac for about 2 hours (yes, 2 whole hours) and be extra sure your r134 cans don't have any stop leak or "seal enhancer" or "synthetic booster" in them as they will just re-damage the system.