I need to make a similar repair. Was considering using Sugru, or 3D printing a new version of the broken off bit and epoxying it in.
Not sure when I will have time, but the 33 "Teletype" metal faceplate looks easy enough to make out of an aluminum sheet and the printing something that wouldn't be hard to clone with a laser cutter and some Cermark.
That stamped radius edge on the modem blanking plate would be a pain though. I'd be inclined to mill it from bar stock and paint to spec if the original paint can still be sourced, but that gets a bit more pricey.
- Gillian