The upper part is interchangable, but the bottom part is a seperate piece from the doorsills on the 94-96s. The only issue is color. The 91-93s have a one piece doorsill and bottom pillar from the hood release to the side panel at the rear seat.
I do not know what part you are referring to "package tray carpet". If you mean the package shelf behind the rear seat, I believe they will fit.
It depends on what yours look like, and if you have paint. The others will cost you about the same as a can of matching paint, and you do not have to do the work. You have to have front and rear doors open to remove the trim. When you remove them, take the upper seat belt bolt out (T55 and breaker bar), pull the bottom out a about 2-3 inches, then pull down on the part, or you will break the upper clip attachment. The upper clip hooks under the pillar near the top.
i have paint... but i was only wondering if i got the b pillars from the 95 b4u, could i just swap them in. basically would the 95 b4u caprice b pillars be a direct replacement in a 92 caprice... the b pillars that i have dont have any damage whatsoever. im just trying to do a color swap. the only reason im considering the other b pillars is to avoid painting.