Burke & James No2 Ajax portrait aperture question

[pjd]

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?

[pjd]

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

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.