Well , last question first ... there are still homes (alot in the Mid-West) that have fuseblocks in-line with the house current , so , since these units are considered non-conductive (not true when they'd get set in a puddle) , they could still function for the designed purpose .
The 'dubious' part of it is that these commonly contained amosite fibers (one of three types of asbestos) , which people nowadays are not so fond of .
Not to be used as a 'play' pliers by the youngin's !
Yours looks 1960's (or even 70's) construction to me , esp due to the rivets holding the thing together .