Hi, after reading through the E30 M42 chain replacement guide, I stumbled upon the same problem for my E36 M42. The damn A/C compressor bracket that bolts to the block covers a 10mm bolt that needs to be removed to get the lower timing cover off.
What you need to do is unbolt the A/C compressor off the bracket, lift the compressor by the lines, (don't worry the lines are fairly strong) and move it up and out the way. Then you have to unbolt the A/C compressor bracket off the block (the biggest pain in the ass). Then you can get access to the lower timing case.
You will also need to remove the 5mm allen key bolt that holds the crank sensor in place. (this can also be a bit a pain).
Good luck.