Neil, I used to have a 1m dish and twin LNB/selector switch for the old Astra 19deg.
Then I went to Digital, thinking I could put the Digital on one LNB and keep the old analogue on the other. My supplier said it could not be done. Not believing him for a minute, I got in contact with an old friend of mine who installs this stuff for a living.
Truth is.. It can't
You'd have to have two dishes; the smaller sky digital dish, and a regular round 0.8 - 1m dish for the analogue. My district doesn't allow consent for multiple reception equipment, so that was that!
Hope this helps!!
I MISS DSF!!!