It should work fine. I have what was originally a SBC transmission behind the 6.0 LS in my work truck.

The LS uses the top center bolt and not the first bolt right of center on the Bell housing. The SBC uses the first bolt right of center and not the top center bolt. This is probably the difference.

In my application I've just left the one bolt in the difference removed. You could do the same with the adapter, or just drill one extra bolt hole and recess for the bolt head. Could be done at home with a hand drill as the bellhousing centers off of the two locating dowels, not off of the bolts.

You would also have to source metric hardware to work with the adapter instead of the (I assume) imperial hardware that would be supplied to work with a SBC.

 

Morenj,
As far as getting the GM stuff to talk to the Rover side, you have several options. Arduino should allow you to translate GM to Rover. This requires you to program it for that. Another option is to keep the Rover sensors that are necessary to retain functionality of the systems you wish to keep. Likely, you will not find anyone who will just take on the wiring. You will need to figure out how/where you have things laid out and what you plan to keep in order to lay out your wiring properly. Remember that Gen 4 LS engines will require a pedal position sensor with no physical connection of the pedal to the throttle body. Most of the information you seek is in research of how the Rover and GM operates, and talking to people who have done it. Each person I have talked to about this swap has taken slightly different approaches to each challenge. Be honest with yourself about how comfortable you are with the work involved. Let me know if you have any specific questions.