If you up-cam, and you do not install headers/free-flowing exhaust, you could be leaving over 30hp on the table, and a lot of torque will be lost, thru-out the entire rpm band.
If you intend to run log manifolds, I wouldn't waste money on a cam. The factory 5.9cam is a good street cam for the lighter weight 71 Scamp.
However, my notes say that the truck 5.9s had their cam's installed severely out of time, on purpose, to limit pressure, to prevent detonation.
If it was mine, I would change that.
BTW;
IIRC,
1) the early Magnums still had provision for mechanical fuel-pumps, and
2) IIRC, Hughes still offers akit to convert them to mechanical pump, but you'll need a timing cover with the pump-mount.
3) If you ditch the serpentine system, you'll have to change waterpumps too, for two reasons;
a) the serpentine pumps run backwards, and
b) just try and make the gasket seal, lol.
There's a few threads that detail this swap.
4) from memory, the 5.9 cam is; chit I forgot, I'll be back