My 5.9 into '68 Dart swap

Well been having trouble finding the right belt. All I've changed is and a/c delete pulley which is the same size as the a/c pulley and in the same location. And the van style p/s pump mount.
Thought I could just buy a belt for a van and it would fit, but too short. Bought the biggest 7 rib belt I could find 101.3" its still just a little short, even with the tensioner pulled all the way over it wont quite go on. Thinking of buying an 8 rib belt, cause I can get a 102.5" or a 103.5" and cutting one rib off the edge. Seems like kind of a hokey way to go, but I really don't know why the van belt is too short.
Help from anyone who has switched to the van style p/s pump mount would be appreciated.