Also as Zee0Six pointed out a while back, the 9688 and 7317 are almost the same size. (I always assumed they were a bit larger.)
The 3 have the same gasket/ bypass, but while the 9688 is larger in diameter, it is slightly shorter than the 7317.
I use the 9688 size in the garden tractor though and it just fits. I worry the 7317's additional length would rub on the hood.