How about a body lift? That plus taller coils will give you a bunch more room to work with.

A suspension lift may be necessary even with the oil pan change. I am concerned that it would only give enough clearance until the suspension travel is used up. I do realize now that I should have taken a measurement of the clearance between the top of the differential and the bottom of the oil pan. If anyone can measure that for me I would be grateful. Stock 2000 DII with coil springs.

I ordered an F-Body oil pan and LS3 center dump exhaust manifolds today.

I think the LM4 manifold will either hit the frame rail or exit so far back that it will get into the cats. The Corvette LS3 center dump is similar to the Rover manifolds, so they should be a better fit and will be shiny!

Find a BMW V12 and put it in like this guy did:

In on this. I'll be doing an LSx swap of some sort when the 4.0 gives out. Given the LSx to Rover engine ratio out at the shop.

The overfinch rrc and p38 had Chevy 5.7L v8s in them. So this kind of swap has been done before. There is some info on rangerovers.net

Has anyone considered the Audi 4.2 V8?

Transmission-wise, I dont know what the difference between the ZF4HP24A and regular ZF4HP24 is, but maybe its a simple swap?

I always thought Overfinch RRC used a GM engine and tranny, I'm guessing a turbo 400 with a Borg Warner transfer case.

The Overfinch was a 5.7 bolted to a ZF. They used the TPI intake and tubular headers. I found a picture of the bottom of a Overfinch P38 and you can see the ZF tranny pan. It's crazy how much difficulty there is associated with fitting a small block Chevy in a Discovery given that it has essentially already been done. Overfinch even integrated the new ECM with the Rover's BECM (supposedly). The magazine reviews indicate that the marriage was less than seamless but at least they ran. Until the driveline broke.

The adapters from Marks 4x4 look like the way to go. The Gen III V8's have the same bellhousing bolt pattern as most other GM V8's so the small block adapter should fit. List of GM bellhousing patterns - Wikipedia, the free encyclopedia
You will probably need to work out the issues surrounding the flexplate and torque converter on your own. For control of the tranny, that is going to be tricky. The older ZF's would shift without any input from the ECM but I don't know about the later ones. ZF Autobox issues Using a 5-speed would be much easier.

I recall one of the Landrover mags had a article where ashcroft put a ZF behind the puma Diesel in a defender. I recall they used the stronger ZF24 internals, but the older valve body and compushift. I'll see if I can dig it out and scan it for you if you want.