Campy has a differnt cog spacing than Shimano so if you are putting a Shimano compatible freewheel on the back you will need to replace the Campy rear mech or switch your shifters to friction only. I wouldn't mix Campy and Shimano drive train components, you are asking for headaches. AS far as the tooth size is concerened are you worried about the rear mech chain tensioner being stretched too far? It is very possible, but if you stay off the large front and large back at the same time you should be ok. DOn't let anyone else ride the bike without telling them about this gear "quirk" though.