I will go a little opposite, if you don't mind
#3 Yes that extra grey wire goes to the tach. But for the MSD6AL you will have to connect the tach wire to a female provision, which is located opposite of the box's wiring.
#2 The orange wire goes in the brown wire's position (positive +) and the black goes in the black striped yellow wire's position (negative-). I may be wrong but i thought that the brown wire should be a dark blue but anyway.
#1 There are two brown wires because the one has power when engine is in START position (meaning you turn the starter, not ON position) and the other is the wire that goes to the ignition coil.
Off topic, in my car i deleted the ballast resistor and connected the wires alltogether.