Couple questions about cam/springs

Never heard of anyone trying an LS rocker on the Magnum heads. SB Chevy is the usual swap, some guys say the SB Ford is a little better. If the LS rocker pivot length is good yielding proper geometry that will be sweet.
I'd set those heads up for BeeHive springs, as the combination of high rocker ratio and aggressive hyd roller lobe profile is a recipe for a valvetrain control nightmare. Reducing valvetrain weight will greatly improve the engines ability to rev clean. Fortunately the Magnum heads have light weight valves out of the box, so you're miles ahead there.