here are my thoughts. i know i had another hi panel years ago because i was planning on making hardboard and recovering to match oem but found the offset clips and lack of correct shortness staples made it a bitch and gave up after doing one panel. i have black plastic that i will use in the 76 instead.
pighead says the extra warped set of lows aren't his so we think they came out of boss hogs 78.
i know the ones in the 76 are correct, they are high.
i know the 69 had high because the metal portion is the only part that's left (because a screw is stripped and will have to be drilled to get it out).
i think the low panels that i have for the pickle (72 or 73 or 74, i can't remember what it is) may have come from uglibus, which was a 78. i thought no way originally, because uglibus had been converted to a convertible and was sitting buried in snow when we picked it up, but i also got some parts from mike aaron shortly after he got rid of uglibus and may have gotten these panels then.
that said...i know the low panels match up clip wise to early models as i've had them in the pickle. i also know the lows match bosshogs 78 (which makes sense). they match the few holes that i can see on the 69, but the 69 has foam tape to dampen the wood panels that were in there and i haven't pulled that off to see if there are more holes underneath (the 69 appears to have less holes than later because of the tape)
so, a decision is to make the panels to match the high metal panels and the late model folks would have to convert, or make the panels to fit the low panels and the high panel folks (which there are more of) would have to modify, or make them completely flush (for no panel), which i think would be just fine because all the panel appears to do is allow a touch more room to keep the hose from contacting and rubbing and it seems well enough spaced anyways and anyone worried could modify and put the cover on.
another thing to keep in mind is early models didn't have the vent in the cargo panel. that would have to be like the ashtray, left empty and 74 and up would have to cut if you wanted to do a universal panel.
shown are the 78 filler, followed by the 69 filler