Here is a close up of the lens. Miller used this same lens on at least one other type of civy lamp. But I don't know the application (Lex gave me one once).
I have picked up a couple of these other type by mistake (Corgi I think) But they are about 1/4" too small on diameter. But with the correct lens and rim it's easy to glue it in place in the body. Ron
Here a picture of the back, you don't really see the rivets:
Ps, you can butcher a Lucas mounting plate, exactly the same, except the 3 rivet holes, trade you the tubular bit for the plate Dave, have a quantity. Lens not required.
I was thinking of getting the backs laser cut from sheet, I also looked at getting the lenses made, I'm not sure if I should just knock up a couple more, or get a small batch made, the main problem is to find the time with all the day to day jobs in my workshop so I'd have to sub contract the job out, not sure which way to go yet.