IPKnate

I have a new Kyosho Inferno gt2e. I want to switch the center diff out and replace it with the a set of gears like on the Ofna road car, so I went on RC monster where they sell a convertion kit that allows you to use revo gears, letting you go to bigger gears. The problem I'm having is once I set everything up one of the shafts are to long for everything to fit, I know this probably is a simple fix but I'm new to the game so I'm asking for help. Also if there any other ideas about getting faster for drag racing I'll take all ideas. Thanks.