Greg,
I can't advise re throttle bodies I'm afraid. You can retain the carbs and go to a 3D ECU (I think the latest MBE is the 967) but this will cost in the region of £400-500 new (you also need a new wiring harness and throttle pot which adds around £150 IIRC).
I considered this but decided to go the easy option and just find a second hand ignition-only 906. My spare is one of these, but has a different connector from my current 12-pin plug, which would have meant a minor re-wire. Untried, but yours for £50 if you want it (comes with a dizzy and coil).
Cheers,
Howard