1967 Barracuda alternator upgrade question

You can put a 200 amp alternator in, but it will only put out what is needed. In your case maybe 40 amps. No need to bypass the gauge. Add a 10ga wire from the alternator to battery stud on the starter relay. This will allow some current at the ammeter to alert you should it stop charging, and shortcut most of the current back to the battery.