In my opinion, not worth the extra $. I had an old Callies crank which I cracked. Bought the Dragonslayer, and it was not as nicely finished as my old crank. That is when I learned the new Magnum is the same version as my old crank. I think it had Stealth on it. Anyway, I see no reason for the Magnum unless you plan on making serious power and really turning that engine.
Since you already have a big block snout on the crank the dragon slayer would be plenty. The only reason i went with a Magnum in my small block is because the dragon slayer didnt offer a BBC snout option and there was no way i was going to run a sbc snout with an F2 side slinger.