I have first hand knowledge of his six day routine. When I started thats what they had me do. It was great... Its like a crash course in Vince's techniques (but being so young I didn't know any better). And no it wasn't easy... there was some "new" muscle sore on me everyday.
My understanding was that Vince felt that beginners who were brand new to bodybuilding tended to have all kinds of energy and excitement. He started people off with a circuit-type training style that did 1 set per body part the first week, 2 sets the second, 3 sets the third. If the person had so much energy that they wanted to do it every day, he let them. This was for a beginner, mind you.
However, for Vince's intensive training routines he stressed 72 hours recuperation for a hard-worked muscle.
The training consisted of a whole body circuit using a combination of machines, free weights, and body weight. One exercise per body part, for one QUALITY set, minimal rest (just seconds)- and then another exercise.
Initially the training was difficult but do-able. The weights were light enough so that I could learn the movement, yet heavy enough so that I was approaching failure near 12 reps. We used higher reps (20+) for legs, calves, and forearms. I did no ab training.
After the first week I would do the circuit twice, and then later a third time. Other guys were doing two-a-days... but since i wasn't old enough to drive I only went once a day.
I can't remember how long this went on for, but it was a while - long enough for me to want to go the "easier" split routines.