Campy index shifting
It looks like Campagnolo did make an 8 speed freewheel, but it seems like there isn't a good source for old freewheels or compatible cog spacing ones. 

There are plenty of Shimano-compatible freewheels in 8 speed that are easy to find (made by sunrace among others), so this is likely what you're going to end up with. So, for the rest of the answer, I'll assume the freewheel is Shimano compatible. The same things would hold if you had a cassette. 

In order to adapt the Campagnolo shifters+derailleur to work with the freewheel, you'll need to throw a JTek Shiftmate 1 into the mix. Or, if you're only getting the Campagnolo shifters and using a Shimano derailleur (&lt;= 10 speed road, &lt;9 speed mountain), you can use a JTek Shiftmate 4. 

For full details on all configurations supported by JTek Shiftmates see this link. 



Now, also note that you may run into some issues with putting the freewheel onto the bike. 

While the threading of the freewheel onto the hub is going to be the same, you need 130mm rear spacing (which if you have a steel frame and have less spacing, you'll can spread the frame). You'll also need enough axle length to be long enough. You might also need to re-dish the wheel and maybe play around with some spacers. Also, note that 8 speed freewheels are more prone to breaking axles than lower speeds. 

Depending on what you're comfortable doing at home, you may want to leave this job to the bike shop depending on how much needs to be done.