Insisting on running pusher fans, the "proper" clearance unfortunately will be cut-and-try (literally, in a few cases!) Pusher fans are most efficient if they closely approach the radiator core, but due to wind resistence, the blades or fan mounts will flex at speed. This happened not only to a street-driven Pantera as I said, but also to Mike Drew's 427 Cobra replica, using the 'stock' front pusher fans originally specified by Shelby. Mike caught the blade/ mount- flexing during a sportscar run with us a few years ago, before holing his radiator, but even today the scars are quite visible.
But no matter what you do, pusher fans will never approach shrouded sucker fans in effectiveness of cooling. I suggest you make two light aluminum straps 6" long, tilt the radiator fwd and bolt the straps to the rad mounts and the stock body mounts. The stock fan mounts can easily be removed by drilling a few spot-welds out to provide tlit-fwd clearance. The Fluidyne then attaches to your radiator pipes with two 90 dergree 1-1/2" copper 90 degree sweat-solder fittings, $3 each, from any big hardware store.So far, your total outlay is at most another $10. The much more efficient sucker fans with a shroud (Flexilite for instance) also attach to any rad core easily, once there's enough room to get a hand in there. I documented this, with photos, in a POCA newsletter a couple of months ago when I replaced my 20-yr-old brass radiator (tilted fwd in 1984) with an aluminum Fluidyne.