5.9 Magnum out of manual truck going to work?

B&M sell a flex plate to solve this issue.

^^THIS^^ LA engines have weighted torque converters to fully balance what is essentially an unbalanced engine, like a 360LA

Magnums are different. They use neutral balance converters, with weighted flexplates.

You cannot use an LA weighted converter because a 360LA is weighted different than a 5.9magnum, and so on.