Which electric fans work on a C3 with an LS swap, and will the stock alternator keep up?

Here is what the documentation says. Each point links to its source; details depend on your exact computer, harness and transmission.

• The Derale 16749 adjustable fan controller operates one or two fans with a combined maximum continuous draw of 25 amps, has an adjustable turn-on range of 150-240F with turn-off preset 10F below turn-on, includes a ground-circuit relay, a 3/8-inch NPT probe, and an A/C override circuit. (Derale Performance)
• The Derale 16749 fan controller is not compatible with 2-speed OE fans from Ford Contour, Ford Taurus, Lincoln Mark VIII, or Dodge Viper. (Derale Performance)
• Painless dual-fan relay kits ship in two temperature variants: turn-on at 205F/turn-off at 190F, or turn-on at 185F/turn-off at 175F. (LMPerformance (Painless retailer))

Confirm against the instructions for your exact parts before wiring. More: Other wiring in our tuning guide.