Fantastic, all now fitted and OK, as advised quite straight forward albeit a little fiddley and tricky, especially with my huge "Schrek" hands
Firstly, lower the front window as far as it will go BEFORE you remove the door card and with it the electric window controls
After careful removal of the door card (don't forget the screw in the interior door pull....

) there are two screws in the foremost area of the window frame, undo these, and carefully remove the rubber window channel seal
There is a bolt towards the bottom of the door, undo this (although it didn't matter for me, the whole channel fell apart at the top)
Carefully feed the new channel down the door, taking care not to snag or trap any wiring down there
Refasten the bolt, and screw the bracket back into the door frame, then guide the channel rubber back down into the door and reattach onto your new wing mirror bracket.
There was no need to dismantle the window mechanism or central locking system.
I took the opportunity to clean up the wiring for the lecky windows, now the two front windows glide up and down now as they should, not just the driver's as before.
I fear the rears will have seized, judging by the stiffness of the doors themselves and the "unsat in" appearance of the rear seats, I suspect the rear seats on this car have rarely if ever been used....till now
Anyhow, a job worthwhile, it's surprising how much I missed that mirror, and how often I (subconsciously) used it....
Jay