1967 Barracuda alternator upgrade question

If the last photo is the alternator you presently have, it looks like it has 1 field wire (other brush is grounded), as was typical for round-back alternators, but some late ones (~1971) did have 2 field wires. If true, you will need to ground one of the field terminals on your new square-back to work with your older Vreg. Many many posts on this. If your battery stays charged, your alternator is sufficient. I still use the round-back on my 1965 Newport, w/ electronic ignition and TBI (electric fuel pump) and the battery stays charged over a week of driving.