I will be using the Speedway kit to put the larger 11 inch rotors on my 79. This also converts to the 5 lug pattern that I want.
https://www.speedwaymotors.com/Mustang-II-Complete-11-Inch-Brake-Kit-Ford-5-x-4-1-2-Bolt-Pattern,2008.html

Turns out it comes with single piston calipers for late 70's to early 80's GMs like the Grand Prix, etc.
Been doing some searching and have found dual piston calipers available for those cars. Might even be more, but that is what I have found so far.

So I am wondering if it is worth the extra $100 or so (obviously depending on which I get) to go with the dual pistons?
I will also be looking into getting better pads.

I won't be changing this stuff until after the car is on the road, so I may find that I don't need to make any changes, but might as well find out what is what now.  My ultimate goal is to put a 351C into this car, at that point this stuff will become more important. 

Thanks,
Russ