I thought all the bolt heads normally had a number - 1 through 4 - perhaps - my memory is not good on the different headspacing bolt heads.

Edit - just checked my Mark 3's.

#3 on the sporterized mil-spec (only have an action and sporterized (poorly) mil. stock, and the other is full stocked SMLE w/matching numbers, stamped ENGLAND on the front action ring & also stamped 1953 with a #6 bolt head. The stamp is at the front on the right, down side of the bolt head.