Changing Campy index downtube shifters to 'only' do friction shifting
I'm not familiar with those shifters but perhaps this will be of assistance: Campy Syncro 2 shifters

The left/front shifter is a standard friction shifter.
To convert (the right one) to pure friction, you can actually just remove the springs and optionally the boss collar -- the springs are all that is required to (re)move.