AFAIR GT3 was not built on ex-LMS Class 5 loco frames with level top edges, more like BR standard frames with profiled tops.
They were similar in overall dimensions and coupled wheelbase to an LMS Class 5's, but specially made. GT3 had smaller driving wheels than the LMS Class 5 4-6-0s --- 69 " dia. for GT3, 72" for a Class 5.
The tender frames were, however, identical to a BR1(X) type and were bought in, IIRC, from BR Derby Works. The tender upper works were built to the then standard C1 profile of a Mk.1 coach and included a toilet and corridor with end vestibule and a gangway connection to the rest of the train.
I was outside Vulcan Foundry gates in 1961 when GT3 was first rolled out in completed form (having been started some 9 years earlier at EE Rugby). It was beautifully appointed, with linoleum and even some carpet on the cab floor.
The rich, milk chocolate brown livery --- lined yellow/black/ yellow like a BR coach --- looked superb. I saw it towed away to Crewe for assessment and start up: I saw and photographed it on test on the WCML at Newton-le- Willows (passing Vulcan's own back yard fence). I can also claim with no joy whatever that I photographed GT3 on its final journey, as a gutted hulk, from Vulcan Foundry to Geo.Cohen's scrap yard in Salford, in 1966.
It was originally conceived by designer J.O.P. Hughes as a way of re-using the almost everlasting steam loco chassis by replacing the boiler, cylinders and motion with a turbine power plant and direct, geared drive.
Alas, its development phase was so prolonged that by the time it was ready for service, BR were already committed to (mostly double-ended) diesel and electric power which required no turntables.
I understand that one of its cab side numberplates has since fetched at auction much more than the £600.00 which Cohen's paid for the scrap locomotive.
© Eddie Bellas 18/2/2000