I'm pretty sure I saw Alidair's G-ARBY departing from R15 at LBA just a couple of days before it's unfortunate 'gliding incident' short of Exeter. So yes - Alidair Viscounts did visit Leeds in the late 70's
On the Dan Air front, I remember it's leased Viscount 700 G-ARIR being used quite a lot around the same period.