That's the thing dude, there is no options!
It's all there, just buy the conversion and build it up!
I would personally use new idlers (you get 1 in kit) and a new diff gear and you'll have a nice fresh gearbox.
Xtreme sell the machines idlers so order one when you order your kit, if you want put in the new Twin Track diff gear they sell too, be nice!
I think Lee Martin runs a brass bulk head at times so you could try this on the B4.1 Vega but that's about it, don't think the team guys run much weight.
Then ask Danny McGee for some set ups and happy days!