If I were to put together an electric fan set up based on a mild SBC 350(275-300HP), turbo 350 and A/C, I would at least have the following. I would start out with a factory V-8 radiator, 2 electric fans rated at 1000+CFM, sheet metal shroud similar to the one shown here(
http://www.pro-touring.com/threads/81150-Electric-Fan-cfm), a controller, a matching sending unit and a relay box.
Start by basically matching the shroud shown above to fit your radiator. On an Eagle radiator mount the primary fan ¼-1/2” below the top of the radiator on the radiator inlet side. Mount the other fan low ¼-1/2” above the bottom of the radiator on the outlet side. The following fans will fit but be tight, Zirgo ZFB12S and ZFB10S, and cost roughly $140 for both. Lay them out to ensure they fit before cutting the large holes. Use small bolts with self locking nuts to mount the fan to the shroud. These two fans should allow enough free flowing air at highway speeds without additional holes.
Next, is wiring your relay box. I used Jegs 10569 relay kit with breakers(~$72), (instructions located here,
http://www.jegs.com/installationinstructions/500/555/555-10569.pdf) instead of fuses for simplicity and on the side of the road fix with no parts to replace. Just look everything over, reset the breaker and see if it works. If not… there is a bigger issue. Set up the kit following the instructions. Use a controller mentioned next to be the fan switch. Each yellow wire, I used a black marker to mark one of the yellows, will run to either the primary or secondary spots on the controller. Solder and shrink tube all butt connections.
Now you have 2 yellow wires in the cabin most likely on the passenger side in the kick panel area. I used a PAC-2750(Instructions located here,
http://www.dakotadigital.com/pdf/pac-2750.pdf) controller that costs ~$115 to control the 2 fans. Research this before you jump to the conclusion this is too much money. You will need a Dakota Digital sending unit PN SEN-04-#(1-8), the 1-8 is different threads and such. All of them are compatible with this controller. Follow the instructions for two separate fans.
I chose these parts based on wanting a full control of the fans. This is the best bang for the buck I could find with a lot of research and did not leave me stranded when I used it on a 355 SBC, Turbo 350 and A/C. 95-100 degree F sunny days would kick the second fan on in town when idling for a few seconds but maintained temperature. I had slightly larger fans but used the dimensions of an Eagle, 4.2L, A/C Radiator for the fan selection. I had enough room for a 14” and 12” S-blade and they worked great. There is no such thing as overkill when it comes to electric fans.