The Formalin "3" is meant to be read as a range of Formalin from 3 ml/l to 10 ml/l, and that is all.

As Mike said, the prehardener will discolor due to the added dyes in films. I am not sure if the film will survive without the prehardener, but if it does, it surely will need either a hardening stop, a hardening fix or a plain hardener bath. At that time, some color processes used a chrome alum hardening bath.

PE