norvil replacement instruments

I have just recently taken delivery of a pair of pattern replacement instruments for my 1969 750. It looks like I will have to machine the original stud mounting tabs off the original instrument pods and even then will have to come up with some method of securing these instruments in place. I don't want to use the bracket that Norvil sells because it looks too far from standard. I had in mind that I would insulate the clocks with inner-tube rubber bands to make them a snug fit and then fit a small grub-screw under the mounting bracket. Has anyone else had experience with fitting these non-standard units to their bike?