If it's a square device about 3" to a side, it's probably an altitude compensation device aka ALDA. It reduces fuel delivery in proportion to atmospheric pressure; meaning lower atmostpheric pressure = less fuel.

If it's in the way of getting to the shut off valve, you can pretty safely rotate it with channel lock pliers. To remove it, there are 24mm wrench flats under the square section and a nut that takes a 27mm wrench on the IP. Hold the 24mm flats and loosen the 27mm nut. At some point you'll be able to spin the device off the IP.

Sixto
93 300SD