I think it should work. If you want specific info regarding use of the Mugen Centax, try contacting Wayne. I talked to him at my LHS about this. He's been running the Mugen Centax on his GT4 for some time. He can be found at www.rcracing.com
message boards. His screenname there is of course 'Wayne'.
Smitty is charging $15 for each shaft, not including shipping. From what he said, they're titanium.
He also makes the front layshaft in titanium also for $15. But the 2 speed shaft he is making is only for use of the Serpent 2 speed.