Can the seat frames from a 73 barracuda be used if covering it with 1970 seat covers, foams and plastic backs?
Or am I on a hunt for 1970 or maybe 71 seat frames?

No, the early seats has springs as part of the frames where the later ones have the spring built into the foam... the cover centers attach to the springs on the frames. Been there and tried 70 covers on the later ones and didn't work at all. Theres a set of frames with tracks for 200 in the e-body classified now and the pics show what the correct frames look like.

71's should work i have two sets of 71 demon seats early Tall button hinge cover thats seperate from the plastic back and mid 71/72 small chrome button with the one peice hinge/back cover. they both have the springs built into the frame and both have the wire that locks both tracks like the one listed for sale.