I made more progress over the weekend - and I finally raised the courage to make the hole in the top for the plate.
I don't know if it's the approved way but I made a template from 18mm mdf for the actual cut. To make that I accurately cut the four corner radii (at 3/4" rad) then placed the plate over that and nailed four battens around it. I then nailed some more inside to give the router something to run on and cut the opening with a 3/4 template following bit (my first buy from Wealden - excellent next day service). I did nick the template in a couple of places but filled and sanded them smooth.
To cut the top I clamped the template in place and ran a groove all around just over 3/8" deep. I was a bit stumped by the actual hole as I only had a 30mm guide bush and a 1/2" worktop cutter to hand which would have left imo too little lip for the plate to sit on. However a wander around the garage produced a length of plastic drain pipe which was a tight fit over the bush and gave me about an extra 3mm on the lip. Several passes around the template at increasing depth soon had the hole done.
The corner radii turned out to be too tight a fit on the plate, I had made them too big fortunately, but otherwise the template was fine. I scribed the corner lines from the plate and then relieved the corners with a small drum sander in a drill - worked great and I got a perfect fit, much to my relief
Here's a picture of it in situ:
A check for flatness showed that my previously perfect top had taken a slight bow but I worked out that the left and right supports were not perfectly aligned and by screwing the top on tight I had distorted it - amazing when you consider that it's 2x18mm thicknesses of mdf. An appropriate shim cured that problem and it is now as flat as I am able to measure.
Am very pleased with the job as a whole and it was a good way of getting warmed up after the winter layoff. I still have to think through dust collection but I'll use it for a bit first to assess the problem. I guess that I should give the thing a coat of something too just to keep it clean.
It wasn't a cheap exercise, the Unilift was expensive but is real quality. I keep thinking that I should motorize it as at 1/32" a turn it takes a bit of winding (cheap electric screwdriver perhaps for the peak of laziness). It's incredibly rigid and am looking forward to using it in anger.
Bit changing is very easy as I fitted an Eliminator Chuck. The top of the chuck rises to just a couple of mm below the working surface and changes are so much easier than with a conventional collet and all done from above.
I've started making a fence tonight based on a micro-adjustable one published in GWW although I can see that this is an area for development. I haven't bothered with tee track for now as I want to see what needs develop.
regards
Colin