There is a YouTube video about the development of a new model for Victa from about 15 years ago, and it revealed that tooling for making an alloy base is only one tenth the cost of making the pressings for a steel base.
I am pretty sure the alloy version was introduced well after the steel base or at least at the same time as the power torque engines came out.
Don't forget the full crank 160 was used on the steel base for a time and I have only ever seen the Powertorque two stroke used on that base of yours.

Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!