FWIW, a 1970 Chevelle should already have an alternator instead of a generator. Generators were about gone from most GM vehicles in 1965, and all by 1967. I'm guessing that you are asking about changing from the externally regulated type alternator found on the 1970 Chevelle to a newer style (internally, electronically regulated) alternator.
If that's the case, you will want to disconnect the regulator on the radiator support and connect the brown wire from Terminal 4 on the old regulator to the "B" terminal of the new alternator and add a resistor as indicated to make the "GEN" lamp on the dash functional. A 5W wirewound resistor should be sufficient for the lamp circuit. There should be a white wire at the old alternator which would not be used with the newer style, and that wire also (conveniently) connects to the old regulator. That wire can be used to complete the circuit for the alternator telltale warning lamp.
Perform the rest of the connections as indicate in the following diagram - The red power wire to the alternator output stud and a second battery wire (or jumper) to the "A" terminal on the new alternator.
