I mallet-tapped the outline of the rugby-ball jack plate with a variety of radius chisels and then used a small chisel to start creating the rebate:
Once it was all level, I rounded the sides, drilled the hole with a 20mm forstner and popped a drop of tru-oil to match the alder before doing a trial fit:
And after a couple of experiments, I had a go at the ebony. The great thing about ebony is that it will sand/polish to a good finish. What I didn't know was whether the brown streaks would behave in the same way. They do
This is after around an hour, progressing through around 15 grades of emery/micromesh from 180 grit up to 8000. Nothing else - just sanding through the grades:
There are a couple of dints that I will lose by repeating the process, but this will be pretty much how the top will finish up.