Going from a 305 to a 350 required changing some of the sensors.  The ones that must be changed are the knock sensor, and the ESC module (which isn't really a sensor).

These have to be changed because of the fact that a knock sensor is "tuned" to listen to the sounds that a certain engine makes.  The "knock" that it looks for will sound different depending on what size engine it is coming from.  Because of this, the sensor has to be changed when going to a larger engine.

The ESC (electronic spark control) module has to be changed as well, because it is what "reads" the knock sensor and relays in the information to the ECM.