Generally, Parkers with factory installed vent ribs or flat ribs
had a flat top standing breech.
There are at least two types of original rib ramps - one with a
wedge cut into the ramp and one without but these both have
flawless factory finishes where they are actually an integral
part of the doll's head.
A factory installed vent rib will not have been
installed on top of an original matted rib.
Most original factory fitted vent ribs had the last three digits
of the gun's serial number stamped on the underside of the rib,
generally between the second and third post from the breech end
and only visible with the use of a mirror.
No roll stamping on top of rib because the pressure of the
stamp would bend the rib between the posts, it will therefore be
hand engraved. The Parker Story lists approximately 860
vent ribs guns in all grades and gauges.