Yes they were trying all sorts of vehicle types and layouts to decide on the replacement fleet - just after the second war they had replaced the last of the pre war fleet (although some were brought back when the Beeches Estate routes were taken over from Midland Red) and the wartime utility stuff - some other operators just overhauled and rebodied their utilities. The postwar fleet (296, 1481-3227) remained static for a while, then they realised the fleet would all need replacing at once again. Several existing BCT buses were modified with more powerful engines, different transmissions (including automatics) and even one with doors on the platform - and there were experimental lightweight vehicles in the fleet as well. Having tried almost everything available, then Leyland Motors came up with a revolutionary idea - put the engine at the back across the bus, and the entrance at the front alongside the driver - and every other bus design became obsolete overnight.
BCT tried the Leyland Atlantean in its early form (3230, [460 MTE] in 1960 and 3231-3240 [231-240 DOC] in 1961) but it wasn't exactly what they wanted - so they 'assisted' Daimer in Coventry to perfect their version, the 'Fleetline', and bought large batches of them in the following years until 1969 when the West Midlands PTE took control (3241-3650, 3681-3880) and they continued with the same policy for some time, by when Daimler had been taken over by Leyland anyway.