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.