I've been down that same road with the "short water pump" that had the fan hitting the Harmonic balancer and put the stock fan blade too close to mount the radiator in it's stock position.
The solution to this problem is to buy an adaptor plate that mounts to the block...you have to drill and tap a couple holes and bolt a 216 waterpump onto the plate. This gives you the proper distance from the stock mounted radiator, raises the pump/fan up so it is centered on the radiator and gives you the proper belt alignment. I bought my adaptor from pre68Dave on this site for $40. and the install took about 30 minutes. You can get the 216 pump from NAPA with either a 3/8 or 5/8" pulley.
Several vendors offer a "short pump kit" at a dear price and I still haven't figured out how they get the proper clearances and alignment!!!
The beauty of the adaptor plate is that when your pump needs replacing you can get one off the shelf at a reasonable price and better yet, locally.
I've got some pictures of the 216 pump and the adaptor plate in my webshots:
http://community.webshots.com/user/Fla54Chevy3100 Hope this helps.
