With good unmolested rigid frames becoming harder and harder to find, it looks like there may be an alternative, and it's been hiding in plain sight.
This is a 1942 Triumph 3HW that belonged to Jun over in Japan, a quick look at the frame reveals a few similarities to the later twin chassis that we know and love.
Pretty similar as you can see, although some of the tubing maybe of a slightly smaller diameter and gauge to later types. Interesting to see that it has the larger top steering bearing and possibly extra gusseting on the lower bearing, this is a feature seen on the rare post '54 rigid twin frames.
B type 6T cases set up in the 3HW frame, using only new engine plates, no cutting or modifying of the frame involved here. The gearbox is the same set-up as the later rigids so no drama there either.
It all makes for a sweet looking roller, and in this shot the tubes definitely look slimmer.
The girders look right, which of course they are, and to my eye the stance is perfect.
Sweet as a nut! A big thank you to Jun for sending the pix and making my day!