When the 16 ga. first came out the bores were at .650 +/- mostly minus. At some time in the early thirties they were changed to .662 and by the early forties the chambers were changed from 2 9/16" to 2 3/4". The early guns with the chamber change had 2 3/4 Inch Chambers stamped below the serial number on the barrel flats.
In Brophy's book, "Plans and Specifications of the L.C. Smith" prints show the choke area at the muzzle to be 1" parallel and then taper 1 1/2" to bore, so you are talking about 2 1/2" of choke area.