I did say 'probably'!
My aspiration is to have a number of semi-fixed rakes of freight (and engineering) vehicles, reflecting the changes in vehicles used, and services provided, during the period 1957-66. Which is why I thought S&T, for use towards the end of this period (when commercial traffic was virtually non existent . But I would not be adverse to a 'newly introduced' non engineering version, particularly if the model is a good one.
Are there photos of the use at Staines Central which you mention?