No problem. Just trying to pay my dues to the forum which has helped me an innumerable amount of times.
Do you know why the pin fell out?
AFAIK it
should be accessible with the valve body and intermediate plate out. I suspect you'll also have to remove the b3 brake band guide along with the b2 piston to relax the pressure on the band. You may want to pull the valve body sooner rather than later to see what else is wrong in there. I would be interested to know what broke to cause the pin to drop. It will not just fall out on it's own. The guide piece is plastic though not necessarily prone to breaking. Did you say the transmission was overfilled at some point?
You may want to try and get mbtechman, Johnhef, or M.B.Doc in the loop since they are certified (or have done this lots of times) as I am not. Good luck!