if you cna get a custom coil made, dual gap space between them 1/2 the height of the topplate(3/8 if you want more b/l which i suggest) the actual coil height should be around 25-30mm a peace.. so if the gap is 25mm spacing between the coils should be 12mm this leaves 6mm of EACH coil in the gap, leaving ruffly 29mm xmax slightly higher because the gap is faily large and once the oppsite coil exits the other coil acts like a normal overhung driver... IMO with such a hih MMS a smaller coil or less spacing between the coils is more ideal.. my oponion would be spaced 3/8 the height of the gap and use 2 25mm coils... that still wil give you 30mm of xmax, pleanty for almost any application, not only thats you could get much better resuls with a ported aligment.. for SQ 3.25 tuned to 28 and 2kw would be a pretty sweet setup... of course this is a guess, but from experence im not far off.. you will see a slightly lower qe from the lowered MMS but chanes are you want a stiffer suspension(not much maybe 2x)..