5 speed gearbox - RENAULT MASTER 2.5 T35?

I am told there are so many different boxes for a Renault Master. My vehicle is a 2000 x reg 2.5 D T35- .... again told that location of reverse gear and starter motor will play an important role. Reverse gear would be where a 6th gear would be. Does this help? Do you know where i can purchase a box or get this one reconditioned?
Regards

CHRIS
November 2009