on the new aftermarket stuff,I have seen where the proportion valve is tucked underneath the MC,but I believe you still need one. The original proportion valve on the tbird,from what I read just goes to the rear brakes and gives the rear brakes less preasure than the fronts. What I'll probably do is use the 67 MC,or a mustang booster since it is more flat and a Granada MC and get a modern proportion valve and plumb it like a modern car.I hope the email link works,not very good with computers.
http://www.ultrastang.com/Page.asp?PageID=18