Sorry, you can NOT use that cam!
That cam uses hydrolic flat tappet lifter
Magnum engine uses hydrolic roller lifter.
IIRC the length of the cams are slightly different as well as journal dia(any LA experts/feel free to correct).

Here is a link to that same cam on Summits site.
Click the applications tab
It lists more details, including the fact it fits in LA blocks in various year motors from 1964 to 1991 in 273, 318, 340 & 360ci.

http://www.summitracing.com/parts/LUN-00043LK/

http://www.lunatipower.com/Product.aspx?id=2423&gid=292

Adv duration is such BS I really dont see why companies list it anymore.

That cam has 292adv duro yet only has 230/230 at 050.
Comp Cam (custom) in my 408 has 286 adv yet has 236/242 duro at 050.

If you like that cams specs
Get a custom one from Comp Cam

Some places will charge similar price to that Lunati but you have to pay cam core charge up front which will be refunded after you send your stock or current cam back.
That is dependant on the grind, it may require a fresh core & cost double with no core return.
New lifters will be extra as well

 

Indy is correct, you cannot use that cam. That cam will be too long for the Magnum block as it is made to drive a mechanical fuel pump. It won't seat in the block correctly.