Clarification on 70+ alternator VR on 68 cuda

What do you give up on? The one field terminal threw me off, sorry if that is what you are referring to, I just did not know what to do about that, was thinking maybe a piggyback blade would work but you guys confirmed why it would not, that is why these forums are so great!
Here, I had to go back further than I expected, but this is a previous round of the squareback /solid-state reg. upgrade.......
Going from pre-70s V Reg to the newer post-70s V Reg Squareback