I don't think Gen 3's came without AC. You should be able to get a belt though. To get the proper length, take some string, rope, whatever, and wrap it around your pulleys. Mark the string to the proper length, measure it, and then get a belt that's about an inch shorter (to account for the tensioner).
Bring that measurement to the parts store, along with how many ribs your belt has, and they should be able to help you. Here's a quick lesson on belt sizing and part numbers:
Let's say the belt number is 935K6. That number denotes that the belt is 93.5 inches long, and has 6 ribs.
If you are trying to figure out why I have taken out the ac its because everything went bad and ford wants about $2000 to fix everything. So I'll look on e-bay and fing the new parts and when I have everything I'll re-install the ac.