You should just need the grill and headlight relocator brackets to swap the newer grill on. The other holes are already there. The 91-93 trucks have a slightly different core support and the headlights sit up and back a bit more.
The truck will look absolutely stupid with the 91 grille in it without the relocators. The headlights tops will be covered and there will be a gap underneath that will look horrible. It's very obvious. With the relocators, it will not really look right (the lights stick out a bit) and you will find it hard to get the headlights adjusted properly. The kit was pretty shoddy for what it cost. Trust me on this since this is how I did it the first time before I wrecked my truck. You will have to also drill extra holes and add spacers.
The proper way to do it is to swap to a 91+ core support. It's not really a lot of work since you can do it with the fenders in place. With air tools you can do it in about 3 hours max. You should be able to pick one up at the local junkyard for little or nothing. I got one for $28. Already did the swap and just waiting for the grille to come in. It's a great conversion and you can't tell my truck from a 92 from the outside since I have the 91+ bumper on the back. I sitll have the older impact strip on the bumper though it looks okay. Just don't waste your time with the relocators...J
Got the grille in a week or two ago. Check this out. This is done properly with a 94 core support from a Blazer. This is what my truck was supposed to look like before the accident. Too bad the stinking after pic is from a camera phone. This is the same truck in both photos. The first photo is after the accident in which the first 92 grille was broken (bent the core support) so this is from an 85 clip.
Don't do this to your truck!! I am sorry if this is your truck, but man that looks bad!:barf: Check out the huge gaps below the headlights. You also have to cut the grille up to make it fit and drill extra holes.