The three Triumph 3SWs on the right have Triumphs own girder fork fitted you can see the Triumph style bottom fork link,the two on the left of the photo have what look like the webb girder style bottom link?,did they fit webbs to some 3SWs too??
I think you are right Steve. You can even see the mudguard P clip on the back fork leg Ah Lah 3HW! The bikes in the middle are Royal Enfield WD/CO's from 1941, so the picture is after the start of 3HW production. Ron