What's really strange is the retrofriction shift levers that came with the mounting band had a larger inner bore diameter. They will go on brazed on bosses without a problem if you change out the mounting bolts, but the brazed on version of the shifters will not fit over the retrofriction clamp on band bosses because of this. You will have to make sure the Simplex clamp-on band will not have the larger diameter step on the bosses to do so.
Found this out when I transferred a set of clamp-on Retrofriction shift levers, on to brazed-on bosses on a project bike.