I can'r remember which company did the T31 model, but I do remember building one, painted as WT919 (my A&B steed at Kirton Lindsey in 1960), flying it a few times with no damage (amazingly) and 'presenting' it to 168 City of Leeds ATC Squadron when I left home to Join the RAF later that year. 30 inch span sounds about right. It was hanging in the ceiling there the following year when I revisited it wearing my JT stripe.
(Edit) after a brief search, my memory was jogged, and it was scratch built from an Aeromodeller 1958 plan, now can be found on
https://outerzone.co.uk/plan_details.asp?ID=2108
F2