is the interior from an 86-87 the same exact size as an 88-91

 

The interior isn't an object... what are you talking about more specifically?

 

the carprt im tryin to put the back seats in a 86 gxl from an 88

 

Ther rear carpets are only slightly different, will work but won't be exact match, 89-89(S5) headliner is not as wide by couple inches, A-pillars different, B- pillars are different because S4's have seatbelt holes in them and S5 doesn't. My advice- remove bins and housing and put the seats in. All FC's have unused bolt holes in the B-pillars for the chest strap on rear seats.

 

Wait a minute, 86, and 88 are the same car. I should read better next time. Just put them in.

 

yup- both are series 4. Bolt right up.