Thanks all for your help!
I went through almost a dozen belts before finding the right one. Turns out it was a 90" belt, Dayco 5070900 worked for me. After a number of frustrating back and forths at pep boys and autozone with the wrong belts, I took
snrusnaks advice and measured the distance with a piece of string. that gave me a ballpark size to work with.
armed with that info I went to the Dayco website, they have a very handy "dimensional" part look up http://www.accessdayco.com/Dimensional.aspx
I chose a few within the size range till I found the right fit.
I learned a few things about belt sizes in the process. the "7" in the part number is the number of ribs and the "900" is the length - 90.0"
The Duralast 905K7 that Shadowmustang suggested likely would have worked as well, as its only a half inch longer, the tensioner pulley should give you a little leeway to work with.