Maunsell 4-Coach sets 241-247 were formed in 1933, all BTK-TK-FK-BTK.
241-243 were composed entirely of high-window stock, however 244-247 utilised older low-window 1sts in the set. As already stated these sets were all reduced to 3-Sets in 1951, with a composite replacing the FK and TK.
Interestingly Hornby were to have produced the High window stock in lined SR livery back in 2011: Catalogue numbers R4506-11 covering six different types: BTK6, BTK4, TK, FK, CK and BCK.
Thankfully (for us pre-WW2 SR modellers) set 243 has arrived in its lined green finery at last.
Glenn