The transmission bellhousing/case is different for the diesel and the gas because of the hydraulic clutch vs cable clutch. Swapping either way is a pain but it is probably easier to go from hydraulic to the cable clutch than the other way as you need specific diesel only hydraulic clutch parts which are hard to find esp. the pedal and bracket. All of the cable clutch parts are fairly common and work well if correctly installed and maintained. Nonetheless, I would stick with the original clutch system and keep looking for the correct part as I've seen several of these messed up badly by a hack conversion that never ends up working right, usually diesels that can't find a part or used trans.

To make it even more confusing there are also differences among the gasoline transmissions 2.0 vs. 2.6 which have different cable clutch parts that aren't compatible but look almost identical.