The trunk lid will fit although the 73 up used a different lock cylinder configuration so you will have to use the 74 lock cylinder. The front bench will bolt in (you may have to use the right seat track from the 71 because the later model floors changed a little to accomodate a converter. This affects buckets more thana bench, so you may be ok.) The biggest problem with the front seat is that the 4 door bench seat doesn't "fold down" to allow back seat access. If yours is a SPLIT BACK bench, this can sometimes be fixed by removing the side hinge cover and removing the "stop" that keeps the seat solid. When you do this, the seat will come forward anytime. You can run it that way or you can remove the latch from a two door seat and make it correct. (That is a LOT of work)
Finally the BACK of the rear seat will work. I think that you will find that the BOTTOM of the back seat is too long and will not allow enough legroom.