What sensor and wiring differences are there when swapping an LS2 in place of an LS1?

A Gen IV engine differs from Gen III in the sensors the PCM reads: a 58x crank reluctor with a gray crank sensor (Gen III: 24x, black), a 4x cam sensor on the front timing cover (Gen III: 1x, at the rear of the block), EV6-style injectors with USCAR connectors, and drive-by-wire throttle. Many also have AFM and/or VVT. So a Gen III PCM and harness won't run it directly. Use a Gen IV PCM and harness (or a 58x-capable aftermarket ECU), add a DBW pedal, and plan an AFM delete if you're changing the cam.