The accepted way to use GM rockers on a mopar magnum is to drill and tap the stud holes in the heads to 3/8 and use screw in rocker studs instead of the magnum press in style.
With any spring pressures over stock there is a possibility of the press in's pulling out of the heads.
Also magnum studs are 5/16 and Chevys are 3/8 (probably the ones you have are for a 3/8 stud.)
But yea, using Chevy rockers on a magnum is common.
