I think I've got an early model equalizer bar laying around, and I'm fairly sure that they are not the same (not to say that you couldn't adapt and overcome)
If you look at the V8 versions (easy to find) then the smallblock V8 equalizer bar is the same arm arrangement, it's just the pivot bar is longer on the 6 version (I won't say they are the exact same, but close enough for you to be able to figure out what the differences are)
You have a wider engine bay by a smidge, the pedal assembly is pretty much completely different, and I would bet that the firewall has the through-hole in a different spot. Because of those I doubt you could easily interchange them.
If I remember correctly, the 67/68 bar, the bars going from the pedal-rod and the fork-rod meet in the middle of the pivot, whereas the earlier ones essentially just go straight up and down. This should make the '67/68 bar slightly more stable than the earlier ones