In the '60s I had a book called Scrambles and Motocross by Les Archer which I found very inspiring.
Of course I lent it to some-one [as you do,] consequently I don't remember who, and haven't seen it since, or another copy anywhere.
It was probably indirectly responsible for a few monumental get-offs by me at Moorebank!
I believe that any-one reading the book now would find it quite interesting comparing the type of machinery that was winning big time in Les Archers day, to the modern high performance and light weight equipment now.
cheers pancho.