Hello Charlie, like you I haven't had much luck finding info on the C&S tracked tractors. I think one of the few mentions I've come across online is from this (somewhat poorly-written) website:
"In WW1 they set up a subsidiary company Clayton Wagons at Abbey works, Lincoln...
...This was followed in 1916 by a 4 cylinder gas-kerosene engine crawler tractor ("Chain Rail"). This 40 hp. machine lasted till 1929. They also built an 100 hp. gun tractor similar to a Holt machine."
The Museum of Lincolnshire Life in Lincoln has a 1917 Clayton crawler tractor on display, with mention that they were "used for hauling gun carriages in WW1", but I suspect this one has more agricultural origins than military.
Kevin
-- Edited by 11th Armoured on Tuesday 25th of May 2021 01:56:51 PM
The smaller C&S tractor (presumably the 40hp 'Chain Rail' tractor, if the first reference I quoted is accurate) is really quite small - definitely much more compact than the Holt 45, but that could be the large radiator & roof on the latter fooling the eye a bit. I didn't measure it, but I'd estimate that the bonnet height was about at my eye-line (give or take), which is probably 5ft-ish; the length being not too dissimilar to a typical '40s/'50s smallish farm tractor from memory.
W^D Models have one in their range (WDMT14 at the bottom of this page):
I don't know if you've seen it already, but this webpage has a photo of one of the small C&S (35hp or 40hp depending on sources) tractors towing a heavy bomber
It appears that The Museum of English Rural Life at Reading University has an archive of C&S ledgers & production volumes, which may have pertinent information: