Campag's 7 and 8-speed index systems used the same spacing, so you should be fine from the point of view of the shifters. If your mech is from before the days of Synchro indexing, you may need to change it for a more modern one.
If you want to use an 8-speed freewheel, you'll want a longer axle, a longer spacer on the freewheel side, and the wheel will need re-dishing. It's not a big job if you know what you're doing, but you'll end up with a hub that's a touch wider that it was before. Most 7-speed systems are around 126mm, while 8-speed went to 130mm. Unless you're frame's something exotic, you can just spring it a touch and slot the wheel in.
Calmes dans le demi-jour
Que les branches hautes font,
Pénétrons bien notre amour
De ce silence profond.