I'm afraid I've been reading Ahrons again. In his chapter on the broad gauge engines, he mentions the convertible 0-6-0STs, and all the ones in your photos match his brief resume. But your 0-4-4T No. 3548 is one of a batch Nos. 3541-59 that he says were built in 1888-9 as 0-4-2 saddle tanks with 7'0" coupled wheelbase and 9'6" to the trailing wheels. He says 'these engines had a tendency to "waggle their tails" somewhat' and that the last engine, No. 3560, 'came out with short side tanks and a t