This thread is a bit old, but since I know a little about the topic I'll add what I can to be helpful.
First, as far as getting the optimal tune for your E30 M42 which uses Motronic 1.7 (and likely the E36 version which uses Motronic 1.7.2), check out Sssquid Tuning. The owner and I spent a couple of years reverse engineering the M1.7, and I am confident in saying that no other commercial tuner has as much knowledge of it (if only because no other tuner cares much about it since the M42 is not very popular). So, your best bet for an optimized performance tune is Sssquid. Also, I have no affiliation with the company and recommend it only based on my personal experience working with them to optimize the tune for my 2.1L M42.
Second, DIY remapping is not a simple task, at all. Even if you were to know where all of the maps and constants are, how to interpret them and how they interact, you really do need a dyno + wide-band O2 + EGT probes to get it right. I had the WBO2 and EGT probes along with a significant data logging setup, and I still went through close to 30 revisions with Sssquid via remote tuning (they send a modified BIN, I go out and collect data and send it back, then repeat). We got probably 80% of the way there like that, but really getting it settled required live dyno tuning (and I was lucky that someone with the same engine build as me was local to Sssquid and in need of tuning). So if you want to try to DIY just for the fun of it, that is fine, but an off-the-shelf tune is ultimately going to be 75% cheaper than trying to DIY it since a WBO2 + EGT + logger + dyno time will cost far more than a chip.
If you want to nerd out, here are the threads where I detail the M1.7.x reverse engineering projects:
Motronic 1.7 - 
http://www.m42club.com/forum/index.php?topic=19542.0Motronic 1.7.3 - 
https://www.r3vlimited.com/board/showthread.php?t=420029Note, I will not provide XDF files or other BIN/map info since much of it was done in collaboration with Sssquid, and as such it is not 100% my information to give away.