I had the opposite problem with the 340 in my Duster. Yes, I know, it's a Duster but it actually uses the same 26" 3 core Champion radiator that was intended for an E-body. Even though it's a .060" over 340 with 9.8:1 compression, ported 308 iron heads, and a Lunati 60404 cam I was running too COLD when I was just running a mechanical flex fan (no clutch). Took forever to warm up.
Anyway, I got a set of electric fans courtesy of a 1995-2000 Ford Contour. Dual electric fans, high and low speed, with a shroud that fits the 26" Champion radiator like it was made for it. These fans flow 3500 cfm on the high setting, which is more than all but the most expensive aftermarket set ups out there. A lot more than Champion's set up. To get it mounted I added a couple of 1/8" by 2" aluminum bar, and used the original mounting brackets on the fan.
I actually bought the fans new (Dorman 620-104) because the plastic fan shroud section always seem to be broken on the ones at the yard by some yahoo pulling other parts, or maybe because they're so crammed in there on the Contour's. But I went to the local PickNPull anyway and picked up a spare set up (with original Bosch motors) that had the complete harness still attached. Even though the shroud was broken, the price was worth it just for the harness, the fan connectors are like $12 each new, and you need 3. The entire set up is routed through a Dakota Digital controller, PAC-2750. It lets you program all the on/off temps, uses my autometer water temp gauge sending unit, and even allows me to program the fans to run after shut down for up to 5 minutes (and kills the fans if the battery gets low.
http://www.summitracing.com/parts/dak-pac-2750/overview/I did have to buy an extra relay for the dual fan set up
http://www.summitracing.com/parts/dak-rly3/overview/Anyway, the final product. Fan installed with 180* thermostat. No more flex fan, more horsepower, and shorter warm up times. No overheating issues either, even when it's 100*F out the fans still cycle. I did also install a Tuff Stuff 100 amp alternator, which you can see in the pictures as well.