True, the jr's and sr's can both be had in iron or aluminum. The Sr's have 2.02 / 1.6 valves and 64 cc chambers, the Jr's have 1.94 / 1.6 valves and 58 cc chambers. The Roush 200's, of which i have a pair are basically just reworked Sr's. In fact i think it was more of a marketing change (putting Roush's name on them) than it was any drastic rework.
As far as telling the Sr's from the Jr's if they changed the valve size in the Jr's then you'd either have to find a marking on them somewhere or measure the runner volumes ... the Sr intake runner is 200 cc and the Jr is 180 cc exhaust is the same on both.
Good luck
