Yes it will fit fine. The only thing to be aware of is that the 67 would originally have single leaf perches (unless they have been changed) I believe and you stated your 68 had multi-leaf springs. The single leaf perches will be shallower and will require either changing them or mounting the rear end with U bolts rather than the factory bolts. The other thing to look for is that the back spacing on your rear wheels wasn't off set to compensate for the width difference in the later rearend. What's wrong with .56s, pretty fun street gear - especially with a 4 speed.
Good luck, Kevin