My understanding the 64-68 will all fit.
But when I needed a frame for my 66 vert, I went to see a friend of mine who's been collecting & selling 65-68 parts for 20 yrs. He gave me an education on the frame tops.
For 67-68 Ford made a minor change to the bow that goes over front passengers. To increase head height, they formed a step into that rail. This gives front seats a little more top height.
Noting when I looked at my 67 frame, yes it is there, that step. Then I picked up a 66 frame from him, no step.