Well after trying the aluminium plate with wood veneer and not liking how it looked or felt as well as difficulties in mounting other parts on it I have abandoned that idea. The last few days have been all about finding parts etc for the focus mechanism. I have settled on two linear bearings with steel tracks. The tracks I will mount on a wooden sled with a brass end plate with a threaded hole for the focus mechanism.
Progress: I have cut a thread in a length of brass rod and cut out a 3mm thick brass plate and threaded a hole in the middle. All works beautifully and this will be the main drive for focus. I am modifying a methodology seen on several different cameras. Instead of rack and pinion focus control each side of the camera I will have a central screw with bearings either side of the plate. This should make for a very smooth movement and simplify construction.
Dimensions are still a bit rubbery at the moment. However the bellows and lens boards have arrived and from those I can now make the wooden ends to suit. I also have to get some film holders as their dimensions are also required for the back of the camera. As they are readily available I will go get those tomorrow.
Fingers crossed all will work out.