Eureka!

Turns out that the firing pin from GPS was the trick.

The gun is a BSA, but the action is similar to the cadet (Same?) The firing pin is center fire with some adjustment made to the "cocking arms" in order to catch the rim. Originally ordered a rimfire pin which was not the correct replacement.
Part was drop in and the rifle went bang from the start.

Thanks for all who chimed in as it was appreciated.

Tom