So, i spent hours last night working on the 70's Brazil tactic - i've found that your base formation does a good job of emulating the ethos of the tactic. Still not 100% happy with the AP's positioning (finding him drifting far too right on attack on some occassions) When he does stay left he's scoring some great goals when the ball is crossed from the right - he is in acres of space when he arrives in the box. Not sure if a PI or positional change will change this - like you i want him inside when on defence.
I changed the BWM to CM-D - found that this gave a bit more stability in the middle, and changed the right CD to a Ball Playing Defender. Other than that i pretty much agree with your thinking on everything else - i too want a reproduction of the real formation/playing style...
looking forward to your updates
Oh and for the record - i am scoring some amazing goals with this tactic, very Verde-Amarela