Thought I'd close the loop on this.
I bought an '84 seat and cowl. They fit without a problem on my '79. The hinges line up and the rubber feet rest on the frame rails.
I don't have the fender installed, the rear tray mounts to the fender, correct? The fiche only has one fender PN, so I think that'll be fine.

I also got a '79 version tool tray. Since it's taller, the seat won't close, butI don't see any reason I can't cut it down to fit. This tray was a freebie, and has a big hole in the bottom that was repaired with duct tape, so I don't have a problem with "modding" it.