Ford Repair: serpentine belt sizes, crank pulley, ford mustang

Question
my automobile is a 1985 ford mustang,two door hatchback.It has a performance crank pulley,no smog pump pulley.What size belt is needed for application? The belt that's on the car now is making the idle arm bottom out.Too long.

Answer
http://www.netstang.com/whatsizebelt.htm

This site has some good information

If you dont use anything but a waterpump and a alternator, go with a 38-42 inch belt.  Buy all the sizes in between and return the ones that dont fit correctly.  I am using a 42.5 inch but its a 351w.  Ide guess a 302 would just be a little smaller.