If this is the gun I think it is (Springfield model 67H), I believe that gun was sold under different names (and model numbers) back before guns were required to have serial numbers. It was not uncommon for these to have been sold new at Sears, and Western Auto - back in the day when Sears and WA sold guns.
The pump-action shotguns are really fairly simple to completely dismantle and reassemble, that is, if you are careful and know what you are doing.
Reassembling a pump shotgun can be a bear if you don't know in what order and exactly how the parts go in. I know, from experience that - if you bull and jam the thing to try to make the pieces go back together - that is when the problems start as you are bending certain parts that were designed to be perfectly straight! I'm thinking, in particular, of the action bar (some have one, others, two) that makes the bolt operate from movement of the sliding forend. The action bar(s) are typically the most difficult part to get in properly and easily. If you jam on that to make it fit, you will most likely have a gun that either doesn't work or doesn't work properly!
Also, many of these old guns have never been completely disassembled and cleaned. Grease that was used back in the 60's becomes hard over the years and nothing short of removing every single part and cleaning it with carb cleaner and a toothbrush will get the parts clean and in working order (especially tiny parts, springs, etc). Add a bit of field-dirt to that hardened grease and you have parts that no longer work properly just due to being so gunked up!