it should fit in a stock 5.9 magnum with only a spring change on the heads.
the 1.6 rocker ratio is what makes it have more lift in the magnum engine.
my pre-mag LA 318 with #302 heads got .485/.487 lift with 1.5 rocker ratio.
stock roller valve gear with comp 901-16 springs.
some of them will feel loose untill you run it and get oil pumping thru them.
mine are all used roller lifters that I have cleaned and inspected. they always take about 20 mins or so of idle run time to get the air pumped out when they are empty.
I spin mine over a good bit with the plugs out before fireing it off getting oil psi showing on the gauge.
I got 3 of the whiplash cams 2 in LA engines and 1 440 flat tappet and orderd up another roller for the w350 4x4 I just brought home.
I love the whiplash cams.