B5 ECU swap?

[foursprungdugtechnique]

I have a 1999 built, 2000 registered B5 2.5tdi. My ECU is a few months too old to be remapped. I have a tuning box on the pump, gives it more power, and driven sensibly I have had 52MPG on a 200 mile round trip (Perth-Ayr and back).
I can't get my cruise control to work, I wired it up, switched it on with VCDS, the inputs all show for pedals, on off etc.
Could I swap the ECU from a newer B5 to get it (a) remapped and (b) hopefully get cruise to work?
Anything I may have missed with the cruise control, all I have done is as above. No other modules, boxes or anything to connect to or fit?

 

[aragorn]

Later ECU's will use IMMO3, and IIRC trying to pair an IMMO3 ECU into an IMMO2 cluster doesnt work. You could have the IMMO deleted from the newer ECU i guess.

The cruise needs enabled in the ECU using VCDS.