As far as I can tell, the fitting of a small casting has completed construction of the chassis. The casting in question represents the blowdown valve fitted just above the firebox foundation ring on the LHS. Ut is a brass casting intended for use on Dave Bradwell's K1 kit, but the exact same valve was used on B1s.

I've fitted it with the operating spindle vertical, Hope that's correct as I haven't got any prototype photos that clearly show the valve.
I could now paint the chassis components and re-assemble or could start the detailing work on the body. Mmmmm.
Dave.