Thanks for your input guys, I guess I have just run out of talent
I tried to duraweld an alli box on to my cut down manifold but could not get enough heat in to it. I guess tig welding is an alternative but I would need to by some bits to upgrade my welder and then learn how to tig weld. I think using an original and redesigning the bonnet looks favourite at the moment, at least the runners would then be of the correct length. I hope I can find a replacement manifold without too much trouble.
Best and all that,
Dave.