73-80 vs 81-87 interior differences

[xbanone]

I am using an 82 cab on my 76 restore. I have all of the typical issues worked out, the wipers and hood hinge holes. When it comes to interior, i want keep the 70s style dash and instruments. But i will be using new carpet, insulation and seals. My question is, what do i need to know about the firewall insulation, the carpet and the doors seals as far as 73/80 or 81/87. I am assuming anything related to the cab should be 80s, but i want to eduicate myself on the differences before i spend the money.

Also, the seams to be a breakdown on years for 73-77 and 78-80 on guage bezels. What is the difference there?