belts, pullies, bypassing blah blah blah...

I can't say how much shorter the belt needs to be but the underdrive crank pulley is about the size of a stock water pump pulley. I had a set a while back.

This wont help but i just installed a March underdrive pulley kit on my car this weekend . Stock my car uses a 84.5 inch belt since i dont have ac with the pulleys its now about 81.5. I didnt have a belt so i just unhooked the top alternator bolt and pulled the alternator out about 2 inches , cut a peice of metal, drilled some holes and extended where the alternator sits. Sounds retarded and looks ugly but hey it allowed me to run my underdrives with the stock belt until i am able to pickup the right part. I wish the car was at my place right now id go measure the size of the pulleys i dont want to guess at the numbers since you are probably looking for exact specs.. also i dont have any problems with charging or heat.

I think its about an inch inch and a half smaller.

You can always just pull up to an autozone, grab 2 or so different sizes, swap the pulley in the parking lot, and just keep trying belt sizes til you find the right one.. done that a few times after the a/c elim.