Thanks for the useful comments.
Yes the camera has the correct click-in gg screen and I used it to check the rangefinder and scales.

I also acquired a Graflite in good condition, and it clicks onto the Crown.
I am starting to take medium format indoor flash photos , using Pentax flashes in slave mode off camera.
I have modified an old Pentax flash so it is adjustable to chop right down, just enough to fire the slaves.
So for this camera a future project is to make a adaptor that screws into the Graflite to hold the little flash in the reflector.
I will post up results when finished.

In the mean time I am pleased with this 2x3 Crown, and the quality of its initial images.