Burke & James No2 Ajax portrait aperture question

I've just bought a No 2 Ajax portrait lens which has been bumped around a bit. I bought this on eBay and thought it had a slot for Waterhouse stops, but have found there's an internal aperture assembly - with no apparent way of changing it. I've had a look on Google images to see if I can find if something is missing or how it should work, but no luck. I removed the outer tube for the radial drive (which works perfectly), that didn't help. I'd expected to see a slot in the brass aperture ring visible in one of the attached photos for some sort of lever to fit into, but no. Any ideas?

Attachment 184911Attachment 184912Attachment 184913

More searching in old for sale listings at this site brought me to this image of an Ajax No 1: Attachment 184995

Still not sure how that was attached, but guess I'm a bit closer to figuring this out. I was able to close the aperture by gently easing the brass ring around through the case with a screwdriver, but that's not a fix and I can't see how that lever was attached.