I did test work on VALs.
One test was to drive over a hilly route until the brakes faded out (the wheels were small and therefore so were the brakes) and
then continue driving (using the brakes) to assess lining wear . . .
Of course this was done on a closed track (although there were other test vehicles using it, however they
were aware of what the VAL was doing).
The VAL concept was brilliant (if flawed) and it was easy to drive and steer (very manoeuvrable) though you had to be aware of the tail swing - there was a long overhang.
As you state the Leyland 400 was a good motor (and the Telma retarder helped to save the brakes for emergencies).
The Italian Job (the original, not the remake . . . )
http://img96.imageshack.us/img96/7248/bus0134080no.jpg
"Hang on . . . I've got an idea . . . "