No, they are totally different.
you will have to replace.
NO a grill from a 87 will not fit a 91. Only a grill from 88 , 89 or a 90 will fit. They don't even look the same.
no
No
check for vaccum leaks.
73-87 c10 truck frames will fit with minor ajusting
Yes!
81-86 are the same. 87 is the same as the 88 supreme classic. 87 grills will NOT fit an 86 without changing the entire header assembly.
6 1/2"
any 225 sl6 from 1960-87 will fit car or truck as will intake .I have one no cracks call me 250-751-1652
Yes, they will bolt up. If I remember correctly, from 73-87 was pretty much the same truck.
no, the body style changed in 1988 1981 thru 1987 are the same though