Sorry for the delay in replying - the Forum keeps forgetting I've logged in, for some peculiar reason!
I went for the MDF because it seems quite resistant to soldering iron heat. The back of the jig has various holes in it for making up point cranks on axles and the bearing for holding the said crank on the layout, which I'd been doing for several years, and shows no significant signs of wear.
Also the insulating properties of wood/MDF means you don't have to apply heat for long as the brass tube warms up quickly.
Alistair: I assume the article in the MRJ was about the 'Modratec' system? I did look at this a couple of years ago, not long after starting working on the layout, but decided I'd prefer to have a go on my own - eventually!
I shall try something out in due course for the small layout I've built for demonstration purposes at St Albans signal box as that's a bit easier. The locking needs to be visible and overscale so people can see how it works, so I think (hope?) it should be easier than the inside motion on a loco!
Re the switches: Hornby do a 'passing contact' switch in black for solenoid-operated points, an 'on/off' for isolating tracks in green and a 'on-on' in yellow for their colour light signal and other functions.
Peco do 'passing contact' switches for points and signal operation in red, yellow, black and white levers, which of course gives you the three basic colours for stop signals, distant signals and points respectively. As a white lever in a signal box denotes an 'out of use' lever I assume Peco have produced a white one for you to paint as you wish!