I bought this proportion valve for my '81 but their are some differences. The most noticeable is it's brass and on both '81 frames I have they are aluminum. Also the rear port seems bigger on the brass one. Anyone got any info on this? It was listed to fit my '81 not sure about the rear port part of it though? I've already bought new pre bent stainless brake lines, really was hoping for this puzzle to fit without adapting and modifying. ( that was pretty silly of me to think that)