Tell me about your gun, when it was made, and the complete symptoms. I have just gone through building up a 16ga from scratch. I bought an empty receiver from Numrich, the bolt, carrier,slide and side rails from California, a magazine tube from Ithaca, a barrel from Iowa, rescued, recheckered and refinished a stock. Other parts from here, the rest of them from there.
Plus restored a couple other 16ga Ithaca 37's.
I have learned a bit along the way. Maybe I can offer some suggestions.
The one I built is on the bottom, the middle one I am restoring. The barrel is done and reblued, the stock is in process.
The top is my wife's youth/lady size model 1100 20ga.
Yep, they all have the same length of pull. 2 16ga Ithaca 37's and a 1100 20ga. She is my hunting, shooting partner.
In fact, join over here. There is a lot of Ithaca knowledge, a lot, including Walt Snyder who wrote the definitive books on Ithacas
http://www.shotgunworld.com/bbs/viewforum.php?f=59&sid=8802b2b5681b395f633ca26ff018f749