"If a clear enough view can be had..."
Mmm.... I reckon I've found 30+ different period photos of the sidecar side of the Dixon combination, but I'm yet to find one decent photo of the motorcycle side.
Maybe one. Here's a photo (Motor Cycle, 28 June 1923) that SAYS it's Dixon's bike, but I'm not so sure. Freddie used foot boards on almost every bike he raced, but this photo shows what looks to be a standard RA with footrests. Did Dixon use foot boards on No. 55 in 1923? Certainly Freddie's 1924 Senior TT entry was a solo RA fitted with foot boards.
If the photo caption is correct, Freddie's frame was standard RA (with a brazed-on plate for the rear mount).
By the way, the capacity limit of the 1923 Sidecar TT was 600cc, and Freddie's bike was said to be this size.
Cheers
Leon