I actually don't think this is possible without going FWD unfortunately. This is due to none of the donor boxes available having the appropriate IRD mounts cast into the diff/bell housing.
Yes, the ZS180 has the PG1, but to mount the IRD you'd need the bellhousing of a Di to facilitate the IRD, but that itself won't easily pair up to the engine in terms of bolt pattern, and it's not easily altered. Any manual boxed 1.8 or Di FL will provide pedal box and gear linkage. Also, you may need to swap the diff assemblies over from a PG1'd FL into the KV6 PG1 as the splines are different for the shafts.
Or, you could use the Getrag 5-speed box out of a Rover 75/MG ZT V6. A TD4 FL uses this box does it not, so that's your source of pedal box, gear linkage and clutch hydraulics. However, again, in terms off IRD mounts to retain 4WD I can't think how that'd work as no 75's/ZT's were 4WD and have no IRD pick-up points. I'll ponder on that, think I've got a Getrag in the garage at home I'll study. The diff would again need swapping from a TD4 FL manual box.
Also, stop knocking the KV6, nothing wrong with them. The HGF's are mostly caused by leaks elsewhere; waterpump, thermostat or inlet manifold gaskets. That and ignorant owners not checking coolant levels and then whinging when the gaskets do fail as a result! I've got 2.5KV6 in one of my project cars, two GT20rs turbos, stock rover 75 1.8t pistons, rods and liners, bit of lightening and balancing and some head work and I've got 320/330-ish hp and it's only been mapped using the industrial-estate-at-night method so far.