should you be able to install a 4wd suspension lift on a 2wd explorer. What are the differences between them. Has it been done before?

we would need to know what Year Explorer you have to tell you.

i have a 91 explorer xl 2wd, and i would like to put a 5.5" superlift suspension on it with 33" bfg mud terrains, will this work? Does superlift make a 5.5" 2wd version.

If I were you I would look in to a 2wd kit. Mainly cause the one of the major parts of the kit will be different. The I-beam Drop bracket on the driver side is totally different. There are a few 2wd kits out there (Think fabtech makes one). If you plan on useing this off-road you might want to look in to a trading for a 4x4. But Since you have a 91 2wd most likly you have 3.08 Gear which wont do well with large tires.

Good luck.