I'm not a Ford guy at all..that being said..I do know that there were 2 types of Dura~Spark systems. Dura Spark I and Dura spark II..
IF you go with that type of system, you need to determine which will work with your engine..(probably DS I ) .
Dollar for Dollar, and hassle wise..you might want to consider a NEW MSD conversion kit..This way you have Instructions, and know the system is new, (and not sat in a wrecking yard after years of abuse) ,And has warranty. It probably won't cost you that much more either..