you need nothing. you don't need the axles.
Remove the bushing from inside the bell housing where the clutch lever fits in.
Use your B13 clutch arm.
Grind down the block on the lever where it would contact with the vent tube.
connect the switches. either cut the wires and use the b13 plugs that were on the switches, or find some plugs to fit the b15 switches.
As soon as i install my p11 into my B13, I'm going to figure out the best way to handle the shifter rod issue. I'm trying to get started this week. We'll see how my days go...