Is there any difference in the 67-68-69 seat frames?

as far as i know they are all the same, i might be wrong

Some differences I can think of that may or may not matter are that some '69buckets have the springs molded right into the foam for the upper seat back portion and some do not. Also, the '69 seat frame on the upper seat backs have the provision for the headrests. That won't matter if you're not going to have headrests. They'll be covered by new upholstery.