There are two giants in the expedition world- Toyota and Land Rover. It's only natural that their fans would bump heads from time to time. Each has their pluses and minuses. We see all sorts of swaps of Toyota swaps into Rovers, but we also see all sorts of Ford, Chevy, and even... Mercedes swaps into the Land Rover platforms. If it makes the iconic expedition vehicles last a little longer and keeps them from being crushed so China can make cheap knockoffs for Walmart- I'm all for it.
The Toyota axles have many benefits for Series Rovers, mainly because they're widely available, strong, relatively cheap, require little modification, have the option for factory e-lockers (with a little swapping), and offer disc brakes. The cost of building a Rover axle to that sort of durability and functionality is a bit more, although it certainly can and is done.
To be honest, I don't see many people seriously trumpeting Toyota engines as a great swap into Rovers, or any other platform. They do what they do in their original platforms, but when people think swap, they don't immediately run to Toyota. Likewise, I don't see Rover engines as a good swap outside of the platform.
In the case of modern Rovers, often the most economical/sensible replacement is... another Rover engine. As Oilburner mentioned, even those can be an involved and protracted process. Again, the worth of the swap is ultimately decided by the owner, and rarely do they make financial sense in terms of MPG. The math just doesn't add up. However, sometimes the added capabilities tip the scale. Being able to tow, keep up with traffic, or even crest a hill is a major accomplishment that justifies it for some. The Rover V-8s don't seem to have a problem with those tasks, so it comes back to economy and durability, which can be mitigated somewhat through a thorough refurbishment.
I still like the idea of the 4.3L swap. That's just me, though...