I think that the middle pup should be attracted (remember "opposites attract") to both the neck and the bridge.
Just experimented with a loose "North" pup and a Strat with a North middle and South neck (using my handy-dandy StewMac polarity tester). Sticks like glue to the neck, but not much reaction with the middle - not attracted, but not a strong repulsion either... hmmmm. Got a stronger reaction with/against the coils on the bridge humbucker. Might be relative magnet strength.
Do the "neck" & "middle" stick together? If they do and one of them sticks to the TwangBanger, put that one in the middle and the other in the neck (regardless of how they are labelled).
I hope this is right and Robert S. or someone else will confirm this...
Chip