Other than a Euro only 5speed manual, there is no overdrive transmission that will bolt to a 617 that I am aware of.

If you went with a later 60X like cth350 suggested you could try to use a 722.5 or 722.6 with some type of aftermarket controller like whipplem104 does in the performance section. Those transmissions will bolt up, but they won't just work they to will require some creativity. 5 speed manuals with overdrive that bolt to the 60X are also a much easier find than the 5speed for the 61X.