I am unable to view the picture. Do the screws pierce the soft EBB or clamp it?
Looks like the clamp type as on the current Mercury and Nomad.
It's also V and disc brake compatible, with the same seatstay mountings as the current Nomad.
I suspect the belt and V-brake options will have required a stiffer rear triangle than the current Mercury, it also looks to have less tube manipulation, be interested to see how much difference that makes to the ride in reality. No mention of tubeset, I'd be surprised if it wasn't Thorn's own branded, rather than Reynolds 853.
No one's mentioned this is the 40th anniversary model, with the ups and downs of the cycle industry over that time, Thorn deserve some congratulations for still being around!