Derek Piggott is still around albeit aged 87 now. He was very helpful with flight test and tuning information for my own glider, but I would be loath to approach him to research the T53 without an actual need for the info.
Here's a bit more on a T53 survivor in the Isle of Man:
Andreas Gliding Club
There was also A 72" span model of it published in Radio Control Models and Electronics in about 1972. It was that article which made me wonder why I never saw any.