I'm fairly sure the rear section of the housing is the same for gas & diesel, it's the bellhousing (ie front half of case) and gearing that's different. So you may be about the swap a gasser rear housing on, but that involves total disassembly of the trans, and from what I understand these are somewhat complex and nitpicky to put back together right.
Also worth considering welding it depending on what is broken. I've heard of several folks have decent luck welding up cracks and such, so it can be done.