The best thing you can d is measure it with a string. Run it around the pulleys like you would the belt then measure it.Take tha measurement to the parts store of your choice and voila you will have the correct belt length.
Honestly man, they've been pretty cool with me. I ordered about $3k worth of stuff from them when I was in Hawaii and they went out of their way to work with me on shipping wothout me really even asking. It really helps that they're really really into mustangs. Very understanding and cool guys.
Call up Latemodel Resotation. I guarantee they can at least give you a list of what you need. More than likely they'll be able to even source the parts.