Here is a picture to give everybody an idea as to what you have to work with. If you don't modify the crossmember, then you only have about 5/8" to 3/4" of space in front of a single-sheave pulley.
You can modify the crossmember to get more room - which has been done a zillion times. I really pays to mock all this stuff up in the chassis to make some final decisions on how best to address the problem.
IMG_0949.jpg