Well, the question is still not answered, but I heard back from someone who should know. Here's what he had to say about these:
"They were never mentioned or shown in any "factory" training or materials I had,
And I went to Gayden to watch the tub construction using the original Swindon tooling. The fixtures/jigs gripped the parts using the basic shapes, never by threaded studs (which would be terribly time consuming in a production line).
That makes me think the only process remaining would be brackets for securing during shipment. Maybe from Swindon to Abingdon, or just aboard ship...? "