More research while I am away from home for the week and I have finally identified the best option for a Dukedog that might have served the Stratford-Shipston branch. I had previously decided on 3203 as there is a period photo of this loco at Tyseley on warwickshirerailways.com. But more Internet research using the GWR.org.uk site has done better. 3207 was first allocated to Tyseley's sub-shed Stratford upon Avon. Perfect.

The next batch of Bachmann Dukedogs is due next year and I have pre-ordered one in GWR shirt button livery.

I have also given some thought to how the GWR would have overcome the problem of running steam locos alongside the main road south of Stratford. It would have made sense to create a junction at Ettington station with the line then following the Fosse Way south towards Ilmington. A typical winding, follow the contours, branch line. None of this will be modeled but it is important to know that the would be's make some sense.