Bonanza , those engagements under the barrels are refered to as BITES! A "DOLL'S HEAD" is the same as your Greener extention (Cross Bolt) but has no cross bolt, and is rounded on the end so it fits into a mateing rounded recess in the top of the action exactly where you Greener extention is on your rifle. Most Britt doubles have either a hidden, or a doll's head third fastener, while most Euro doubles have the Greener cross bolt third fastener. The doll's head, or greener are better than the hidden third fastener, IMO! I also like side clips!

By the way congratulations on you win at the Big bore shoot! Good show!