Episcope No5 (7 no) and No6 (1 no) fit the first two types of all round vision cupola, as used in Cromwell, Churchill and Comet. The later type in Cent uses No 7 and 8 ISTR. They look very similar but are slightly fatter. It might be that there is no 8 and they also use a 6 but I would have to look it up!
Having looked it up, I was right. Easy to pick up the wrong ones at a show......