Re: 64 Evinride Sportwin Kicking out of gear
I think that you can use the unit from any of the low profile 9.5s from 1964 to 1973. Not sure that the innards are 100% interchangeable between years, but as a unit, they should be.
Is the housing for your unit in good shape? In particular, the bearing area right under the pinion gear. If that is true (round) and the shaft has no slop there, then you can probably re-use the housing if you find innards. That tends to be where the wear first, particularly if you get water in the unit. The bearing wears and the gear starts going off center, followed by the gears going out. Yours looks like the clutch dog cradle came apart, so the housing may be okay.
FYI, there are several 9.5 lowers on eBay right now...