Okay. (Hopefully) Final Update:
Love, love, love the 550i ssk lever in the N55 135i. Short, tight, positive. Gets the UCP (in central "sport" setting), MDP Cold Air Intake, and AP Exhaust, sing in unison on every up- and down-shift.
However, getting there was a giant pain in the butt.
Vice trick had no effect on that steel rod. Mostly because it would just flex inside the plastic mounts in the upper lever.
Lever is in car at this point, but here's the setup I wound up using to straighten it out:
Even had to drill a hole toward the front of the press. With massive lag bolts tightened all the way down at the rear position, the thing still wanted to pull off the header before the lever arm gave way.
Here it is, installed "backward", in the neutral position:
And here it is in 5th, with plenty of clearance for my knuckles:
Found a used trim ring because the forward tabs were broken previously and the one nearest the I-Drive controller gave its life for this little exercise. Should arrive in about a week. But the old one actually still snaps in there nice and tight.
Looks like the longer, leather shift boot is about 2 weeks out. Haven't received confirmation yet. Stock one still tugs in R and 5 if snugged down below knob. 1/2" would probably have done, but getting it an inch longer means I've got a little more leeway for cementing it to the ring and zip-tying it to the lever.
Have a few more pics in various stages of reassembly, in Neutral, 2 or 5, if anybody needs to see 'em.