ID these sidelocks please

[Kevin in NC]

I have a pair of sidelocks that came with a project percussion double years ago. They appear to be very well made, new and with a little bit of storage rust. Totally unmarked except for E C & S stamped under the mainspring. Internet search turns up no E C & S lockmaker that I can find. I'm trying to find out who made and/or sold these and what they're worth. I need to decide to either build this gun or pass it on to someone who will. Any ideas out there?
Thanks,
Kevin in NC

z

 

[Phil Coffins]

Those are made for a cartridge gun, note the rebounding feature of the main spring.

 

[brushblind]

Try Edwinson C Green and Sons which manufactured side by sides out of London possibly?