I found a big solution to the ebrake problems for this set up. These calipers are 38mm and there is an upgrade to 43mm from a Taurus of a similar year range. I am still testing it and only put about 2 miles on the truck, but it does have better pedal feel and the best part is the e brake holds on a hill!!
79-04 Mustang Rear Caliper Upgrade (Taurus Caliper Set)
I used the exact set up listed here just bought the parts from the cheapest places. But happy to report it makes. Bigger difference. I assume this will only improve as the pads bed in properly. Hopefully this will help some of you!