The Web site shown above has/had not done a conversion, they took their information from the U.S site, where it's described as a bolt in conversion, no welding.

The U.S guys do cut the transmission tunnel and boot floor and then POP Rivet in patches, You wouldn't get an M.O.T here in that state.

No gearbox will fit without slight tunnel mods, with a T.5 / C4 auto its not much of a mod.

Spare wheel well is in the way of the diff as well.

Mines a 4 speed AOD auto which is slightly bigger.