You can use the current downtube braze-on cable housing stops just the way they are.

The rear derailleur will have it's own built-in adjusting barrel so you don't need one on the downtube. You won't be able to adjust the shifting while riding but that's a very minor inconvenience.

You need a cable adjuster for the front derailleur but in-line cable adjusters are available so you don't require a downtube adjuster. In fact, given Campy's "micro adjusting" (read ratcheting) front shifting, you may be able to go without the in-line adjuster if you do the initial set it up carefully. However, I'd add one just for the security.