As others have said this is no simple modification.
The bellhousing needs to be modified (shortened) as does the prop shaft (and the latter rebalanced)
The gearbox cross member needs to moved rearwards in the car , which means cutting the original one and rewelding it further back. The supporting mountings for the box are just a cradle at the rear (as opposed to the bolts through the gearbox lugs into the rubber bushed fittings) which does allow the whole assembly to slide forward under really heavy braking ( it happened under racing conditions once to John Mac at Croft BUT emergency braking is something that can easily occur at any time on the road)so you need an additional restraint to prevent this.
These are all the factors BEFORE thinking abut the modifications to the box itsel, as noted above.
In short , it can be done , but it does require a substantial amount of work, money and time, so if you feel like going ahead great , but don't underestimate this as a project.
Good luck and let us know what you decide.
