Many thanks to Andy for permission to use these pics.
I’ve not seen any adverts or catalogue entries for these cabs but I have seen a larger version of the cabs in a 1979/80 Bell Musical Instruments catalogue. The larger versions are known as Aggressor cabs and are rated at 150 watts per pair so I would assume that this smaller cab is probably rated at about 75 watts per pair. So they would make an ideal match for the WEM PA40 amp.
Here is a link to the page referring to the larger cabs –