Seems like you've already identified them. :P
I'm not sure what you're looking for.
According to the internets,
They were budget shotguns. Supposedly the line was discontinued in 1916 when Marlin bought the bankrupt company.The roll markings of Hopkins and Allen Manufacturing Co. was used from 1868 to 1898. Hopkins and Allen Arms Co. was used from 1898 to early 1900s.
Don't know anything about the Springfield. It's a Springfield. And it's old. And, it's probably not worth very much.
Edit: I think the handguard comes off like that so that it doesn't have to be attached to the stock or receiver. Thus, no hinge needed at the pivot point for the handguard. Just a guess from the photos without having it in my hands.