Rather than chopping them, I'd suggest buying lowering springs.
They really aren't that expensive.
Chopping them can create a number of problems with seating the springs, ride height, ride quality, and handling problems.
If you're on a budget, get 'em one at a time from a Ford Racing Wholesaler. when you hav ethe fronts, put those in, and then do the same when you get the rears.
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Woe to him who builds his palace by unrighteousness,his upper rooms by injustice,making his countrymen work for nothing...Does it make you a king to have more and more cedar?Did not your father have food and drink?He did what was right and just,so all went well with him. He defended the cause of the poor and needy,and so all went well...But your eyes and your heart are set only on dishonest gain,on shedding innocent blood and on oppression and extortion. Jer 22:13, 15-17
Above link has them from 140 - 296 for the entire set.
NOw if you're looking something even less expensive, I'd suggest eBay or maybe see if a local parts retailer like Autozone or Pep Boys has something they can order.
Or go to www.froogle.com and search for Mustang Lowering Springs
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Woe to him who builds his palace by unrighteousness,his upper rooms by injustice,making his countrymen work for nothing...Does it make you a king to have more and more cedar?Did not your father have food and drink?He did what was right and just,so all went well with him. He defended the cause of the poor and needy,and so all went well...But your eyes and your heart are set only on dishonest gain,on shedding innocent blood and on oppression and extortion. Jer 22:13, 15-17
Ford Racing Parts online. You can also call your local Ford dealer to see if they are a Ford Racing Parts dealer. I would suggest getting the part number online then call the dealer.
Lowering my stang: chopping springs? 
