Well, your modelling licence is huge, since what you will be modelling doesn't exist and never existed anyway,
I looked up what Hornby call a B set, and they call it a 'GWR Suburban B' if that helps you to look up on eBay, etc, for examples. However, now I know that you are to model a preserved example line, the non-corridors are not usually brought out (if the line has any, that is) because the guard cannot get through to clip tickets, etc. Also, I was at Didcot last Wednesday and rode in a Collett gangwayed sunshine compo, but the toilets were locked out for sanitary reasons, of course. Didcot can run non-corridors very happily, as the rides are free, once you are in the centre, so no need for ticket clipping.
One final point on the Hornby gangwayed bow enders in a preservation setting. Sadly, the C54s, D95s and E127s are not noted by their presence, as most of them are hulks, dreaming of their eventual restoration, in the sidings. They were mundane when they were created and clearly are thought so now, the effort going into exotic super saloons and the like. In fairmess, for lines like the SDR, WSR and Didcot, they will want to run dining specials, so I think that is the reason for the B-E standard coaches' place in the restoration queue.