Hi Barry,
Excellent work with your Triang based cut and shuttery. I have done similar to some old Triang models to produce an original Blue Pullman, I didn't go to the extent of replacing the cabs though. The rear section of the power cars have had part of a first class parlour car grafted onto them and the kitchen cars are made from the other end of the parlour car and parts of the guards section of the power car about the double doors, the first class parlour cars are unaltered.
As you mention the underframe details have been altered variously using bits of underframe details suitably repositioned and with the odd scratch built bit here and there.
For windows I used Finescale's flush-glaze, the toilet and kitchen windows were abraded with fine wet and dry and also the edges of the window apertures were painted black which gives the representation of the window rubbers.
The bogies are altered Hornby Mk2 for the parlour and inner end of the kitchen cars with Lima class 73 bogies for the power cars and outer ends of the kitchen cars.
Paint is Railmatch and the transfers are HMRS.
Gibbo.