JKM

I need a little help here. I've got a transmission out of a 91 coupe that I'm putting into my 84 GSL-SE. Normally all you have to do is swap the tailshafts, but on the S5's there's a big hunk of metal on the shaft that prevents vibration, and I need to get that off so that the FB's tailshaft will fit. Problem is...I'm not sure how.

I've removed the speedo gear and all the snap rings that were in the way, and I got a friend to help me remove that gigantic locknut, and it's still stuck in place. In the FSM there is a piece in there that is labeled "Taper cotter" that is still on there, and I'd imagine that needs to come off before I can yank the vibration piece off. How might I do that? Or is there something else I'm overlooking in pulling it off?