I'm actually converting the front to disc brakes, so a later model prop valve would be appropriate. The ones that were on the mid 70's and up cars were distribution blocks with proportioning valves built in (that were not adjustable - they were set to a specific ratio). However, I won't be using this type of prop valve since I'll be leaving the original distribution block in place (and plugging the hole where the rear line used to be). I'll be using an adjustable one, inline from the MC to the rear line. Like this:
http://www.ssbrakes.com/commerce/det....cfm?nPID=8341