Recomended flex plate and torque converter for my 5.9 magnum engine

Sorry if I sound like a dick when I say this... again...

Everything

Go to a torque converters website and be shocked at the amount of info they ask to get the best converter for your cars application and what you want out of it.
IMO, my home town guys rock, click below on Pro Torque;
ProTorque High Performance Drag Racing Torque Converters
And Pro Torques converter order form;
ProTorque | Free Torque Converter Technical Analysis Service
There is also some very good places below and more not listed;
Dynamic Converters // Pro-Formance Transmissions
Torque Converters for Drag Racing - Ultimate Converter Concepts

Of course you can just go to Summit racing and order a off the shelf 2500 converter.