In answer to your first question, pull the snap rings off the airbox and loosen the clamps that hold it on the MAF. Unplug the MAF sensor so the wire does not break if you drop the thing. After you pull the top off the airbox, pull the filter out and see if the silencer is there. The smog pump is located under the alternator. If it is bypassed, the belt will not be hooked up to the pulley.
In answer to your second question, underdrive pullies should be fine. A lot of people do not recommend them though because they slow down the accessories. I don't have them because I know of people having headaches when they put them on.
Yes, your a/c will get slowed down. The bigger pulley will slow down the a/c pump and therefore the output of the a/c. The subframes may help you out if the squeeks are caused by rattles in the chassis. However, there are many things that could cause squeeking in a fox. Most would recommend subframe connectors anyway because they help stiffen the car up.
You don't have to take apart the whole filter assembly to check for an air silencer, just reach up into the fenderwell and feel around for a big plastic horn.
You don't have to take apart the whole filter assembly to check for an air silencer, just reach up into the fenderwell and feel around for a big plastic horn.
Good point. I didn't think of that because none of the four fox body Mustangs I have had came with them. Actually, I never even checked on the parts car that I had cause I ended up getting rid of it instead of pulling it apart. Now that I think of it, I don't think I have ever seen one in person.