Not an expert but will try and help. The Field Grade with the straight stock would have been a special order, and might have cost extra with the fancier wood. A Research letter might not show it having a straight stock. The recoil pad can be replaced by a period reproduction.
If the 3E is a double trigger gun, the stock would be measured from the center line of the front trigger (not at the curved bow) to the end of the wood and would be close to your reading. With the butt plate, they were usually 14-14 1/4". The center bead should be ivory and pressed in. There are replacements for those from Midway. http://www.midwayusa.com/product/764305/lyman-shotgun-middle-bead-sight-11-press-fit-ivory?cm_vc=ProductFinding