If you care about originality and how the motor looks to be correct for a 1991 LQ1 car, you would want to stay within the 91-92 model year. You can use a 93 motor as well but the dipstick and tube is the only part that is a lot of work to swap over.
1991-1992 Lumina Z34, (standard with the LQ1).
1992 Lumina Euro 3.4, (standard with the LQ1).
1991-1992 Pontiac Grand Prix GTP, (standard with the LQ1). SE, GT, STE trim, (when optioned with the LQ1).
1991-1992 Cutlass Supreme coupe or sedan, (when optioned with the LQ1).
ANY W body that has an X in the 8th place of the VIN will have the LQ1.
Now...if you don't care about how correct the motor looks in the engine bay, you can go outside the 91-93 year range. The 94-95 motors will work but you would have to do some swapping over of parts to make it look correct. Some things are easy, some are not.
The 96-97 LQ1's are dramatically different in appearance and functionality/engineering. They will get you more power but again, lots of internal and mechanical differences. These motors are also interference compared to the NON interference motors from 91-95.
If you have any other questions, please ask us or you can PM me personally as I've gone in depth with these motors during my cars restoration efforts.