I'd use clamp-on stops, but understand your preference. I would just use epoxy and skip the drilling and tapping. I don't think the tubing will be thick enough. My memory is that those old Raleigh frames had tubing thicknesses between 1.4 and 1.8 mm. If your machine screws are 32 tpi then all you would be able to tap is maybe 2-3 threads and only if your tapping was perfect. I'd guess that hand tapping would result in a very sloppy fit. You'd be better off using self-tapping sheet metal screws. In either case, the epoxy would hold the screws in.

Good luck