hi gary,
I've researched quit a bit and have found absolutly no answers to your question on barrel interchange. it's not uncommon not to have a serial number on the barrel since most are interchangable because of various chokes used. i did find an interesting artical maybe you haven't seen.
http://www.warboats.org/mst2Bremmer/Stoner_ord_notes/
stonerhtml/ITHACA_Model%2037_Shotgun.htm
sorry i couldn't be of anymore help,
kim