From a PM, in case anyone else needs the information.
"73-76 are the same lower legs, 77/78 K and 750A (and early F models), look the same as the 73-76 but are taller, the seal area is at about tire height, a bit more stable and easier to get a fork-brace.
trees from 73-76 are the same, 77/78 K and auto have different offset.
leg assemblies from all years should fit all triple trees, as long as the trees are in sets."