I have one long walkway TTA, I have to agree with you that I have not been able to find an exact match to the wagon...
Hi Richard,
I have gone through all of Paul Bartlett's photos which are available on line... reading Tourett (revised) there does seem to be a number of SMBP tank series which do not feature in that photo stream, this is a pity as the photos in Tourett suggest that some of those missing SMBP / SUKO numbers could be good for the kit.
Pugsley has provided a new reference source, see post no.#159 above, and there are a couple of possible wagons in that collection. Please do not be fooled by some of the photos which look suitable only to find that the non-ladder end has take-offs for kerosene...

or that the walkway is only on
one side of the barrel

. And then the most annoying detail of all - a long walkway, on both sides of the barrel, no plumbing on the non-ladder end of the barrel... and V-hangers which are outside of the solebar and brake gear which bears minimal similarity to the kit

.
Pretty close to a "Not Like The Real Thing" kit.
regards, Graham
So look for SUKO 67955, Esso 66316 and BPO 60778...

.