Cutting the e21 platform down was a mistake. As usual, trying to do things before hand to make it go faster and easier did exactly not that. It should have been left just as it was stock, as once in place it was already too short to make any minor adjustments. I can see no logical reason to use Jakeb's mounts and shorten the e21 platform. That said, I was exasperated at making it work, getting everything in place, and then finding out I could not install the pin on the selector rod/selector rod joint. The half-moon shift platform bushings and their mounting bolts (that go into the tapped transmission bosses) are in the way. So, I found two more e30 airbox bushings, chopped the shifter platform down to just the area around the cup, and mounted it up. I trimmed down the e21 foam piece (it has a metal core) as well to fill the void. Now it's a semi-rigid body mounted shifter, which I will probably be much happier with anyways. (The trans mounts are Delrin.)
IE 5 speed conversion clutch line is in hand, looks like it will work perfect. Fluids will be the last thing in of course, so not officially tested.
The selector rod is indeed 8.5" (216mm) center-to-center, using Jakeb's mounts.
The adapter I will not incorporate unless the tach doesn't work when it's up and running. I am hung up on a couple details in the wiring, as again I am seeing conflicting info.
#6 on the c101 is listed as the M42 ECU Power in Jakeb's list, however in the wiring diagram this is listed as "12V to Diagnostic Connector from Fuse 11 / Ignition Switch". This leads to pin #16 on the Diagnostic Connector. The white main relay which is incorporated into the engine wiring harness already, is what I believe powers the ECU.
#15 is skipped over in Jakeb's list, but in the wiring diagram it's labeled "Engine Starting Signal" which seems odd to ignore. This goes over to the Starter, at contact 30h.
The rest is very straight forward.