see Here Robert Tuck!
One is a Lucas SSU700P/1, The other one a Dominator? but no Medallion hole had a PRS8 switch and Ammeter in it but sadly no Chronometric speedometer!
I have a genuine one in my Dunny store ,bought to replace the battered one on the bike. Not got round to it, at current rate of progress (lockdown lethargy) may never. I can send a photo to a phone ,but others will post something for you.I think the Lucas part number is in the parts list.
Just put a magnifier set on the headlamp shell with Ammeter hole and PRS8 switch and it has Lucas MCH 61 on it.
Done research it is a BSA A65 A50 unit, Lightning or Cyclone application, if I drill a hole for a Medallion who, but me, would know?
A really zealous rivet counter?
Don't worry- it definitely won't be me!
The light switch hole should be on the left and Ampmeter on the right.