Sorry, been away from this thread. It is indeed a Vitus 979 - I have one and it's a lovely bike. Arguably the peak of '80s aluminium. A word of caution - or two...
First, I have heard rumours that they can come unstuck (they're held together with some kind of resin, apparently). Mine's rock solid, and I have no doubts about it, but I thought I'd mention. Second, check to make sure the deal includes the wee screw that holds the seat post. Vitus, being French, had to do things differently, so their seatposts are held in place by these little screws -
and if you don't have one, they're near-impossible to get.
There's a good page about 'em
here.