Need help with speaker specs. Which is true

[Old Guy with 87 GT]

in my 87 the doors take 6.5s ,the back ones take 5x7s and the dash takes 3 1/4s............be aware of the depth of the speakers you buy.........
i have 6 1/4 infinity's in my doors ,the depth was to deep so i had to mount them on the surface of the speaker covers,............
i have 5x7 polk audio speakers in the back ,they fit in the factory opening fine.........i originally put 5x7 infinity's in these opening's they fit but the clearance was tight for the magnit's.........
also have 4" infinity's in the dash ,but had to do some modifications to fit them,i had to inlarg openings and loosen up the smalle defroster ducts that are below speakers for depth clearance

well good luck hope i helped