Dont get 70714 its the layshaft for the center one-way. I'd strongly suggest against using a center oneway.
If you want purple spur gear hub this is the one you want....
http://www.hbeurope.com/piw.php?lang=en&partNo=61324
Grub screw should be z700, you will probably need 3 one for each center pulley one for the spur gear hub. (Make sure you loctite these grub screws in).
If you can find the layshaft in a store look at it. I think they now make it with holes so you might be able to use the plastic spur gear hub and center pulley for the rear.