Thanks for all your replies guys... very efficient.
All in all it seems like it could be possible then.
I will pick up a double chainset and a road mech, keep my XT 8 spd Cassette and Sachs 8spd chain and use my old STX front STI shifter and just adjust the limit screws on the deraileur.
The chainring/chainstay clearance is a bit of a worry but as the frame is a skinny tubed steel Orange C16R I am hoping that the stays will not be too wide apart.
The bottom bracket is still a bit of a mystery..... XTR has changed a lot over the last couple of years with their new cups and spiddle designs etc so I might need to investigate further before forking out. My 'cheap' road conversion using parts lying around is rappidly starting cost a bit more, especially with all this talk of XTR!
Thanks for your help so far!!!
Tom