Well, plenty of time to chronicle the build, so first of all, open one of the boxes - the two kits are identical.
The kit is comprehensive, needing only solder, paint, transfers and glue to complete. Put another way, the wheel sets are included. The kits are therefore a little less expensive than others but make up to a similar standard of finish. The sides are pre-formed with the tumblehome and the one size fits all floor can be easily trimmed to match the scale length of the coach. The only riveting required is on the buffer beams and this has been done using a bradall I happen to have to hand. The instructions are easy to follow and a sheet of colour printed compartment photos and mirrors is included.
Why these coaches? Research shows that in the late 1950s, toward the end of steam haulage, the demand for commuter traffic in Warwickshire was changing. Most First Class passengers were switching to cars, given that Birmingham had achieved "motor city" status. Up until his death in 1956 my father had always used the train from the Lakes Halt to Moor Street, but before he died he recommended that my mother should learn to drive, so my own family certainly joined in the rush toward personal transportation. Actually, I am not sure my father even used the First Class option, but clearly those that did were no longer as keen to travel by rail. The upshot of this was that the make up of the trains switched from B Sets in 2s, 4s, 6s and 8s (depending on the traffic needs) to a B set plus an all third non-corridor coach. So the Collett C43 kits have been adopted to fill this prototypical need. When DMUs were introduced they had the same 3 car arrangement.
The three coach rake also fits the shortened platform lengths, a major compromise in the layout.