The 68 has the short seat and sometime I think in 69 they went to longer seat. This is what my memory tells me. Doug Wilford could tell you for sure.
Yes, the 68/69 seat are the same. It is the short "saddle" type. The 70/71 share the same seat, the longer style. I have, on occasion, seen a shorter seat on the earlier 70 model. I have also seen only one longer seat on a 69 model. Kinda depends on what the assembly line had at the time. The longer seats are easy to find but the short seats are tough to find in good shape. Some of the short seat pans were made of aluminum, and some were made of steel, the aluminum ones split and failed. You can buy Fiberglas repro short seat bases from RPM racing @
[email protected], these are tough and will last!