I mentioned this project a few weeks ago and have now made a start.  The bodyshell came as part of 4 picked up cheap as chips on the 'Bay; 2 are LMS brake 3rds and the other is a GW C61/3.  E121 is a Collett bowended non gangwayed composite. 

I have acquired a Comet underframe kit, ends, and end fittings from Wizard and began the project two nights ago with the underframe.  This proved almost absurdly easy as there is no need to bother with the solebars, which are preformed with the alu bodyshell.  It was just folding the chassis up and the end boxes, then soldering the end inner pieces to the boxes (cosmetic whitemetal outer ends which you file down to fit to the profile provided by the sides finish this off) , folding the trusses out, and soldering the brake hangers in place.  I have predrilled the central of the 5 alternative bogie pivot holes, and may well be reaming this out further to accept spare bogies from an ancient Airfix B set donor, or alternatively Stafford Road Works 3D prints.  A test fit of the bodyshell went well, and it fits nicely over the Comet underframe and to the end pieces. 

Next task, later today, is to source a piece of suitable stiff card to make the compartment dividers. and to order some Ratio/Parkside seating.  The dividers will give the bodyshell a bit of added rigidity before it is fairly extensively manhandled to scratch the doorway joins and drilled for doorknobs and grab rails.  The window reveals are simply cutouts in the alu, even the door droplights, and I need to source droplight frames; this will give me the opportunity to have some of them open or half open.  Planned livery is 1945-7 GW choc/cream on one side and BR unlined maroon on the other, possibly with different running numbers, and the coach will run with a 2-coach set of Hornby Collet 57' suburbans in crimson livery.  With luck this should be a fairly straightforward project, and I am not anticipating any problems with it; there, that's jinxed it! 

I'm a bit worried about the rigidity of the underframe, which is quite thin brass and wobbles about in the breeze, but it should be fine once it is fixed to the bodyshell.  I will need to take very great care that all is level and square at that stage, which will not be until the coach is almost finished; in fact either this or fixing the cosmetic bow ends on will probably be the final assembly job.  The interior will need to be painted, glazed, first class and smoking labels, and a cosmetic floor attached first, which will seal the interior in forever as there's no chance of getting the roof off!

Any advice about scribing the doors will be appreciated!