Instead of removing the plastic couplers just go to tower and buy them. I made some stub shafts using the revo stub shaft axles:
http://www3.towerhobbies.com/cgi-bin...?&I=LXHFY7&P=7
Just cut off the threaded portion. I don't use them anymore since I'm using UE 8mm cvds so I sold them to a guy in the UK.