I just did my '87 C10 this afternoon. There are three bolts in the engine compartment and one in the cab. Make sure the heater hoses are removed. Check the top of the air box at the back and make sure the computer is not in the way. I had to remove mine to get the proper clearance. Remove all of the ducting behind the glove box. With this all removed you should be able to pull the air box out and down enough to disconnect the control lines and vacuum lines.