Just something from my own experience with the 20 reppers - 8 weeks is a LONG time for a 20 rep squat routine. Typically, if you are starting around your 12-15RM, by the 12th-15th workout you will reach your 5-7RM weight on squats. That's just 4-5 weeks. Taking them beyond this point is tricky. I tried it once, ended up with a pulled lower back at the end of 5 weeks.
One thing to remember though, is that you are using alternate workouts (unlike me, I was doing the 20 reppers 3x week) for the 20 reppers, so you will get to that point slower, and so 8 weeks might be fine. I guess all I would say is dont keep 'n' number of weeks as a target; rather keep at it till you feel your lower back can take no more. It's brutal and effective, but remember, the effectiveness counts for naught if you mess up the lower back.
Dont want to sound negative dude, just sayin temper your enthusiasm with consideration for your lower back. All in all, its a good routine, and even if you can stick for 5-6 weeks, it should pay huge dividends. And yeah, dont forget that bit about GOMAD. Trust me, this part is almost as critical as the routine.
Good luck man, and if you start a log, keep us posted - we will look forward to you getting some killer gains.