Ok it is your lucky day! You got aN allmost DOUBLE efficient alt than the one original from your car. It is couple of milimeters wider than the original one.
That's a laters 70s and 80s alt not the first squareback series alt which looks on a side view the same than your original one. Your car will be HAPPIER with that alt.
It seems the brush for the field is already modified, getting cut the prong and mostly sure the isolation washer being replaced by a metallic one to be grounded. Prong was cut intentionally to not conect the field there causing a short. The earlier setups ( mech regs ) are regulated by positive, opposite to the post 70 alts ( 70/71 roundbacks included ) which get both brushes isolated being regulated by negative.
If you have the stock charging system without any kind if wiring jumper or bypass, I suggest run AT LEAST a wire straight between alt post and ammeter stud at black side straight through the firewall. Time to charging wiring and related parts mantenience