Dear Pete,
I agree that there are many hours of fun to be had making EMU kits. There are some people who quote seven or eight hours to put a 2 BIL together - I'm not one of those and nor are you! The N.N. Bulleid style EPB looks to be of very high quality, although I was surprised that wire held with split pins should be suggested for the roof conduit.
The Hornby class 73 is certainly worth a go. I spent a great deal of time on chopping up the chassis detail between the bogies and creating a 3-D set of underframe components. Mine is repainted from the Fragonset 'Spitfire' model which gives an easily prepared black undercoat for the BR blue livery once the printed names, logos and numbers are removed. Order your set of Ultrascale wheels now if you want it running this year! (They can supply 13mm dia. replacement wheelsets which only require the removal of a small amount of plastic on the motor bogie moulding to accomodate the flanges). The Ultrascale wheels made a lot of difference to the running and appearance of my 73. Out of the box, the model won't run on code 75 track, at least not SMP bullhead.
The constuction of a DC Kits class 74 was subject of an article in BRM a few years ago. Watch out for the bogies, they seem to be tricky..
Colin