Thanks, Redfate,
I've had it sitting on the shelf for over a year. I'd offered it up several times and was at a loss as to why in heavens name it didn't fit.
It was supplied by Williams Morgan and firstly I had contacted them, spoken with the suggested people there and was assured by them that it fitted!
So I then started looking at my car wondering what had moved or perhaps been damaged but alas I found no answer. Posted the question here a couple of times to discover no real solution, but was led to believe that they were made by Cain and he supplied them logo'd to others like BHM. You might see mine marked Williams Racing on the picture..
So I reached the conclusion that it was either my plate, my car or despite Williams mechanic's assuring me they had fitted them to my configured type cars before with no trouble ,it certainly did not fit!

So I would have to adapt the plate to fit my car as I wanted that skid protection that it would give to the chassis cross member.
I offered it up and scribed the areas that needed to be relieved in order to make it fit ,and into the workshop with grinder and files I set too! When exactly as I wanted it, I held it in the correct place with one of my newly made cross head support stands and using the guard holes as drill guides I first spot marked the cross member using a 6mm drill. Then I changed to a 5mm drill and finished the holes through the cross member(5mm drill is tapping size for 6mm). I had decided to tap the holes 6mm to give added security and then use a nut as a lock nut on the back side but on closer inspection I found that the hole on the RHS of the car was so close to the gearbox that with a nut fitted it was just off touching a strengthening gearbox webb so I just installed a shortened screw tightened into the cross member using loctite thread locker on fitting. I'm an engineer so am quite happy to undertake this sort of work although I'd hope if anyone buys one of these plates to fit themselves all that will be required is to drill the holes and fix the bolts! I'm comfortable drilling and can feel exactly what I'm doing and where I am but I would suggest If not you protect the soft gearbox casing with some metal sheet to prevent damage. Something like an old pointing trowel or similar would do.