So, what's the chance of getting the "black box" that makes all of the electrical play nice so we can choose our own engine?
Zero.
If you want emission-legal stuff, Nick Markiw makes the conversion for D1/RRC/D90/110, D2 in the works. It is more expensive, including LS3 and 6L80E, but you get a lot of mileage for that.
Other than that, this conversion is okay for places that don't have strict emissions checks. It would probably fly in 90% of smog check places in California, too - but if you come across a guy who's seen a Land Rover engine, you may fail and it'll be a nightmare afterwards.
Walter - you already have a GM engine in your truck, why do you care for not having another? GM is an absolute, undisputed, king of making the best components. They just couldn't make it into a vehicle if their life depended on it, which has been proven a few years ago.