I found it but not in the normal listing - there are some without photos which I was going to offer but for some reason I looked at the "for sale" section and there it is!
1952 EGS (Eric Guest Special)
JAP engine with Royal Enfield gearbox.
The main entry (without pictures) tells us
Eric Guest built his special in 1952 at Highways Motors in Redditch, the garage which he owned. It used a JAP engine mated to a a Royal Enfield gearbox with Morris 8 brakes