1931 and 1932 have 1930 specs.
Rudge? The 1931 DT Rudge used a very different engine from the 1930 DT. It was based on the 1930 TT engine, so it had different crankcase, timing gears, cylinder, and head (with bolt-on plates rather than cast-in pillars to support the valve gear). Also for 1931 there was an option of the standard 1930-type frame, or a new longer wheelbase version. Despite the fab new engine, even Rudge greats were bolting JAP engines into their Rudges after the first few races of the 1931 UK season - the origin of Victor Martin's "Martin JAP". I see that Martin's early brochures noted that the frames were made "Under Licence with Rudge Whitworth Ltd" - interesting that Martin and Wallis/Comerford ended up under the same umbrella.
I wonder why the Crocker DT machine ended up with a cross-over gearbox. Seems like such a bad idea on paper.
Leon