any markings or inscriptions on the frame, magnet, etc.?
I'd say it's 70s and British made, looks like a McKenzie to me, they used them on 70s Marshalls and Park cabs
here's a pair, they look like yours:

yes, that twin is a very HEAVY beast. I've got a late seventies silverface and an original blackface 65, both sound great but they stay at home, can't be bothered to carry them around, hehe