if you want a single coil, using 500k pots, and want a decent volume balance with the 78 set, id go ssl6 for the middle in this setup.
i love the texas hot and the alnico 2 pro, but with 500k pots they are really bright.
the texas specials can have a harsh/gritty upper mid thing in some guitars, i wouldnt want to hear that with 500k pots