The crank hub is the most importiant part of the drive set up. Your crank hub/pulley length will determine your blower snout length and idler bracket.
If you look reeeeal close in this pic, you can see the spacer between my lower V belt pulley and the blower drive pulley. The stock V belt pulley bolts to the BDS crank hub then the 2" spacer gets your blower drive pulley out of the way. It works just fine, but it makes for a rather long blower snout.
A couple of years ago, I ditched the spacer and modified a single groove flat pulley on the crank hub and was able to shorten my blower drive by two inches. I also had to use a shorter 64-67 timing cover and water pump to get the water pump belt out fo the way of teh blower belt.
This pic doesn't show the new bottom pulley set up but you can see the drive is way shorter.
Good luck, -Abone.