I ran into that problem too with my 451 A-body. Even with the shortest clutch available (Hayden 2947) there would have been less than 1/2" clearance to my radiator core...

If you don't run a fan clutch, a direct drive has two problems - lots of wasted hp at higher RPMs, and possibly more importantly, high fan RPM that could result in a catastrophic explosion.

I installed a Contour dual electric fan. Remains to be seen if it's enough to keep it cool in a hot Missouri summer.