GEMS ECU as standalone in 1989 Range Rover

[TomE]

Greetings from Tanzania!
As this is my first post on this forum I will include a couple of lines as way of introduction. Because of my location one of my leading principles has been to stick to simple analogue cars with electrical things kept to a minimum. This principle always came with one exception: if I ever get a 1st gen Range Rover, it would be allowed to have efi. Having recently acquired a farm and cleared about 7km entrance road to it, now is the first rainy season the road is being tested and it has quickly turned out that the "family car", a 1991 1pz, 70 series land cruiser is too heavy and underpowered for steep muddy hills at our altitudes. So the excuse to get the RR is finally here, with approval from management! (Rational option might be a 300tdi Defender..)

So I have located a 1989 Vogue SE 3.5 efi with auto gearbox. This would be a complete strip down and rebuild of everything. The original plan was to swap the engine for a 3.9 with 14CUX, but I am getting tempted to transplant a 4.6 instead while I'm at it. I have done a fair bit of research on all the forums, but as I am very much out of depth with ECUs I thought it would be wise to post my specific situation for review by the experts!

I understand that the GEMS/Thor ECUs are connected to the BCEM system including body control module, gearbox control module, security module, etc. etc. and that a workaround is needed for the engine/ignition ECU to work as a standalone. For this workaround I cannot find many recent discussions so wondering if there is a simple solution these days? I know Tornado Systems offers unlocked ECUs with chips etc, but are there other options?

My idea is to source a 4.6 engine and use the ECU it comes with. I am not planning performance cams etc.

Using the GEMS ECU would enable keeping the electronic ignition vs using 14CUX and of course the GEMS was intended to run the 4.6.

Also wondering if it is better to source the engine from a Disco or P38 RR? Or does it make a difference?

And finally, am I right in looking at GEMS engines or would a Thor engine be better?

Thank you very much in advance for any advice!
Tom