Might be better to get an S62 engine from a breakers yard for a couple of K. Look to see how different the top end is and possibly do a straight swap. The Block is the same unit... then you only have to worry about the change in throttle body set-up.
I'm sure a UK BMW tuner could help with the ECU controllers... you may be able to rob the original ECU from the doner vehicle.
Alternatively get a doner M62 engine from an old X5 or 745 saloon.. and work on the heads yourself/in conjunction with a local machine/engine shop...
