With that clamp design, I think you will struggle to ensure sliding forces in the rear stays, for example, didn't just allow it to move along the chassis rail.
The other thought I had about bolt fixing would be to drill, fit crush tubes and bolt it through the chassis, 6mm plate either side, with the top plate sitting tight to the chassis above it.
I suppose a lot of the regs are there so they allow proper inspection of the mounts -it's easy to see a 6mm plate welded to the chassis, and easy to see the 4 M10 8.8 bolts holding it in place, not so easy to define or see how a bolted fitting should look, or whether crush tubes are present and indeed fitted properly.