Usually, the short shifter kits have nothing to do with it being a 5 speed or 6 speed.
But you are right, if the linkage is different on the 987's, the one they currently sell may not work. You should inquire about it via their web site.
I sure wouldn't pay the dealership prices on one of these short shifters though
I'd wait until B&M or Schnell comes out with one. Far cheaper.