I think you're getting very close John. The front diamond also has quite a few CL features, like the rear-exiting seat post, and the seat stays that attach a little way down the seat tube. As a teenager in the 1970s I devoured the Vintage Road Test Journals, and remember the sporting Blackburne-engined 1923 CL in Volume 2 very well. The book is still on the bookshelf, and the clear photos are useful here. The detail around the seat lug looks very much like the cafe bike, as does steering damper. No sidecar lugs on the frame, though. But 1923 was the first year of the 545cc side valve, using Chater Lea's own engine. That had sidecar lugs, and they're identical to the cafe bike. No dampers shown on the front forks in the Motor Cycle photo, but production bikes may have differed. A Sturmey Archer gear box was fitted, just like the cafe bike.
I wonder if we're looking at a 1923-4 545cc Chater Lea, with a JAP twin shoe-horned in at some stage, many years ago by the look of it.
Love the CL frames John, but hope you've got more parts lurking in the shed!
Cheers
Leon