I bought this collection of parts, which came with a 1924 0-3 manual and a 1925 4-6 (along with a fair bit of other ephemera). What provoked my interest were the tin plated Slotted Strips, p/n 55. The tin plating has now turned gray, and indicates that the parts were made in the US Meccano factory in Elizabeth, NJ. I think I've seen tin "Architraves", #108, but not the Flanged Brackets (right and left), 139a and 139b, in tin.

The parts may have been a No. 4, perhaps made from a 3 and 3a, based on the manuals.