the serial number would tell you which color is correct, not sure on the seat I guess you could call the person would made it.
http://www.acmoc.org/index.php?option=com_content&task=view&id=38&Itemid=56
On my D2 5U the seat also has two halfmoon washers to hang the seat back from, with two studs lower down to stabilize the back. I believe there is supposed to be two strap hangers (according to my D2 operators manual) to give more adjustment to the back but they are missing on my machine and do not need them for functionality but to be totally authentic they might be necessary. I'm building a new seat back, cushion and armrests and using just the back hangers
😆
My late model D2 has two straps that bolt to the back of the seat and then hang on the upper buttons on the tank. The lower part of the strap bolts to the boss on the lower part of the tank
I thought Highway Yellow was "Old Cat Yellow", as distinct from "New Cat Yellow"? I buy my Cat paint from the local Cat Dealer here in Australia, it's premixed the right color and the price is very reasonable, about $US60 for 4 litres, it is made here in Australia by Wattyl to Cats specs.
The salesguy sold me some spray cans for touch up jobs and he was sure they were "Old Cat Yellow", they weren't, they are "New Cat Yellow", a lighter shade, so I used them up as a undercoat.
regards
Mike