Rear brakes options with SSBC Force 10 Kelsey-Hayes Brakes

I was wondering what rear brakes everyone was running with their Kelsey-Hayes 4 Piston Front Brakes. For my 67, I currently have the most cost-effective Force 10 kit, which is the KH 4 4-piston calipers on 11" rotors and Turbo-Coupe single-piston calipers on 10.5" rotors for the rear. When I ran the numbers for brake bias, I came up with 79.1%, which seems off.

Is anyone running 2015-17 GT calipers or 2005-2014 Mustang rear calipers (both using MustangSteve's brackets)? The front to rear Bias appears to be more variable than the SSBC kit.



Calculator:

thanks.