Hi John B.
I've only just seen this thread, and I did go to one Wednesday session at Brands Hatch in 1966. I was racing a DMW Hornet 250 at the time, and had a friend by the name of Jim Robinson who made a single drum, TLS front brake. He got the DMW factory to agree to fit his brake in the "works" six speed Hornet, and I had the job of testing it at Brands.
The brake worked well, but a small slip-up, in how it was fitted to the forks, caused it to lock on after a few laps, and I came to a juddering halt. The circuit was not busy, and it was a rather uneventful day. I do remember that you had to be very careful on the exit from the hairpin, 'cos there was a small (about 6" dia.) but deep hole in the tarmac! There was nothing to warn you about it, you just had to watch where you were going and avoid it.
John C.