Wrong Alternator?

Depends, LOL. You must determine what type VR you have. The ORIGINAL OEM regulator for 69// earlier used a single field terminal alternator. The later one you pictured will work if you ground either field terminal and hook the rest up normally

If you have converted to the 70/ later "flat" electronic VR then you MUST have an isolated field alternator, sometimes INcorrectly called "dual field." (2 field terminals.)

The second type called a squareback is BETTER because those type normally charge better at low RPM. Again, you can ground one field terminal and hook it right up