This is the first Selmer brand Electro model B I've seen, and I've never seen the amp-in-case setup either.
I have seen Premier Vox Model B Spanish and Hawaiians. As iI understand it Rickenbacher exported the hardware parts to the UK and her colonies before WW2. The pots in these instruments were British and sometimes at least the pickups were also wound there.
I guess Selmer another British company did the same.
Is there a serial number on the top of the headstock?
How does the amp sound?
No serial number anywhere I can find? I've not tried the amp yet, as it has no earth/ground so there's a chance of electric shock. I'll address that issue. But it is in beautiful condition, considering it's age.