As said that film has got a silvermask and needed a process taking care of this. This process was offered by Tellko and exclusive laboratories.
Nonwithstanding Tellko published this masking process.

However for less quality demanding users there was chemistry offered for a more simple process based on the Agfacolor-principle.

It seems Ian has got the latter formula here:
http://www.apug.org/forums/forum222/...evelopers.html