I’m in the process of collecting all the parts to convert mine. From the conversions ive seen people either use the original gearbox and modify the gearstick (gearstick comes out where the puma heater matrix is) and modify the heating pipework.
Or they convert to automatic obviously no gearstick to worry about only the difflock/hi-lo selector.
Or use a discovery box with the selectors further back which means cutting into the seatbox and possibly make a centre console of some kind.
The option ive gone for is a puma galvanised bulkhead with a discovery gearbox. This way i can use the heater matrix and pipework from the puma.