Derale 16" fan will fit on the short SA radiator...as a bonus, you can modify the factory shroud and it all looks factory since you can now hide the wiring under the shroud on its way to the relay or controller box.
The way the Derale is made allows about 4 to 5" to "hang" below the radiator so that the oil cooler is actually getting some action, too. The brackets keep the fan blade off the radiator bottom tank lip just enough to make this happen. I don't know about other fans, but by happy circumstances, this is what I found when I installed a 16" Derale on my 1980 RX-7...I might even still have pictures of the install on the old W98 PC at home. The engine it cooled was a
Rotary Performance Big StreetPort 12A - think Ari Yallon and Chris F. when they still rebuilt 12A's - 135 HP at the crank, out-of-tune, with a bone stock Nikki but big custom exhaust...
NEVER had any cooling issues and this is in Texas Summers where we hit
105 degrees F. "Out-of-tune" because the car got totaled 2 weeks after the dyno session...