freehub and downtube shifters

I have a rear wheel that has a Campag screw on hub. The BB on the frame is
Shimano.

I would like to utilise it as a commute/trainer bike and so would like to
just have a single 42T chainring and use a wide range of sprockets at the
back.

Could I use a downtube friction shifter so that there would be no indexing
problems with the Campag/Shimano setup?

Given this, what rear mech would you recommend for, say, a 12-32 setup? MTB
type?

Many thanks in advance!