You'll need the 3.3 knuckles too - the 3905 or 3.3 drive axles use a diff knuck arrangement, brgs are diff and the TB attachment is diff as well. I don't remember if these will work with the black 3906 bulks - think they won't, theres a raised boss in teh plastic around where the drive axles go that won't let you get the drive pins in. I changed to the grey 3.3 bulks when I converted mine.

You'll need to upgrade idlers in the trans, stock nylon won't last one run. You need to replace the flimsy roll pin in the top shaft that secures one of the gears as well. Its a lot easier to do before you shear it off that to fix it after you've sheared it off! I made a pin from a piece of L wrench as most do. Run the trans in 2nd, theres no need at all for 1st.

RC Monster has good idlers, I'm running UE, but they prob are not available anymore.