This playbill (click on it twice to view larger version) is from the production mentioned in passing by William Russell in the Radio Times interview that I posted earlier today.
I'd love to tell you more about the casting, but there's no information online. The billing suggests that Jackie and Russell played significant roles. If you're not familiar with the play, you can read a fairly basic Wikipedia entry here, and perhaps also have a look at this Guardian review of a modern Royal Exchange production, and make your own inferences about how they may have been cast. I'll update if I happen to find out anything more (at present, I'm awaiting clippings from the V&A theatre archive's "very small" file on Jackie, so you never know).
It's also interesting to note that they were billed as 'Stars of Dr. WHO', and that the whole season was a 'Television Star Season'. I gather this was a bit unusual for the 1960s, in that many theatre producers remained uninterested in casting familiar faces from television as a way of boosting ticket sales.
In fact, in the DVD commentary from the Doctor Who serial The Chase, from which I posted an excerpt recently, there's a discussion about this very point in the context of Maureen O'Brien's struggle to find acting work after she left the programme. Everyone seems to agree about how difficult it was at that time to pick up work after leaving a regular television role, and about how much things have changed.
Radio Times interview with William Russell