I know your exact troubles. I modified my stock ones but it took me nearly 4 hours of trial and error. To save you some time, done use those spacers between the seat and track. The seat will sit way too high,.
Word of caution - when you start messing with brackets/different seats, be absolutely certain all the fasteners you're using are Grade 8 and that any steel you use has enough tensile strength for the application. The forces the seat can experience in an accident with a 100-250lb. human strapped in it are astronomical. Your garden variety hardware store fasteners can fail in shear or tension very easily. The shoulder harness won't do much good if the whole seat comes free on impact. Be careful if you start modifying things.
I know Joe (UnderPressureGT) just installed those seats in his car, and said they were a total PITA! Looks like your best bet would be those seat brackets from Holcomb to save you the hassle... expensive though at 65 bucks a piece.