I believe they have different offsets the width is the same. I have a 70,72,76,77and 78 every top/bottom tripple tree is different. Every one! The later ones (73 to 78) are I believe interchangable but some have a pedestal for a choke assembly and the distance between the guage bolts seemed to change every five minutes. I think you will need the correct lower to make it work. This older style looks like the same one used on a sandcast ask the sandcast gurus which lower you need.