Don't worry chaps, thanks for the offers of help, but I contacted Graeme around a year ago who put me on to his talented mate Mick...
Mick lives way up in the North East but wey-hey man he knows how to work metal... this is what he did...
First an oversize piece of ally was machined from a block...
.. it was then roughly fitted to the frame....
.. tig wleded in and then ground down to size ...
.. and the slit cut in...
... pretty amazing in my opinion.....