I'm not sure which version of the Beta 5 we have, will it be stamped on the casing.?

It looks pretty much the same as this one, although it doesn't have the NEMA photocell socket on it, just a hole that somebody drilled (off centre ) for one of those Royce-Thompson two-part things.

Not sure how to fit a NEMA socket to it, as being off-centre any attempt to enlarge the hole with a drill would be problematic, and filing would take an awfully long time

@Ria @Sammi
It should say on the gear tray if the sticker hasn't deteriorated away. But Mk.15 has a metal clip, Mk.16 has a plastic clip. The older Atlas and AEI lanterns didn't have a level 'turret' to fit a NEMA cell, like the Thorn types do.

This one doesn't have a NEMA, but a 2-part cell like yours. There are four indents on this turret, that indicate where to drill the screw holes for the NEMA socket. If not drilled for a minicell, there should also be an indent in the centre to show where to drill the main hole for the socket.

Yours has a cell turret and a metal clip. It is a Mk.15 which dates to 1982 at the latest, and 1972 at the earliest. You may find a more exact date on the capacitor. Look for four digits EG. 2478

We'll do that, unfortunately somebody has bodged a hole in the top, which will have to be welded up before drilling for a NEMA socket, but we will look for those dates