Based on what I see in the 1960-68 MPC, the "65/" means 65 through *, where * = 1968, so they should be all the same. See the attached picture.
That said, the same MPC says for the fastback (63 body style), there is a 65/66 version, and a 67/ (67 and 68) version. I learned though the other day that there was a change for the 68 fastback, so the MPC is not correct for what was done at the factory. So if you went to the dealer to get a service part for your 68, you would be handed the 67 part, which is quite different...but it would work.
If for some reason the MPC is wrong and the 67/68 version is not what you want, I have access to a dozen or more 64.5-66 models in my favorite junkyard. The part would be cheap, say $30, but I would need to be compensated for time (including part of the 4 hour round trip) and the shipping isn't cheap.