Mike,
The Heym(barrelec action) action does not have a thumb slot.
Has the late FN/Browning style bolt stop. Sadly, those parts are missing. I have acquired FN parts, but the designs are not identical and either action or bolt stop will need modification to be fitted to the Heym.
You can convert them to use a standard mauser bolt stop.
You thread a piece of keystock 1/4-28 then drill & tap the action so it will mount in the same spot as it would be on a standard mauser action. Slot it & drill it for the bolt stop screw to pass through.
