Oh yea. Had the same problem. I had a black magic on my stock rad. Electric fans and old school radiators don't work well together. After switching to a griffin radiator, I only had 3.5 inches to work with. The only fan that I could find on the market was 3.57" deep is made by mr. gasket. At 3" your looking at a 12" diameter fan. Look to see if you can mount the fan lower on the rad. for more clearance. My fan is only 3.57" deep at the very center.
I ran into the same problem on my 69 stang with a 302 and serpentine conversion. I got a Spal electric fan and that worked like a charm. Do a search on the net, I got mine from Racer's Wholesale for only $165. It flows 2800cfm of air(I tryed it, it's not BS!). Good luck!