The problem you have is the alternator itself. You need a different model.
The Magnum engines came with a NipponDenso built alternator. Different dimensions and mounts.
I like this option better, which leads me to a new set of questions.
1. Can i use my old v belt style pulley on these?
2. Are these still externally regulated and if so can i just wire in my two fields to the wires from the connector?