MOPAR Performance Valve Covers Williamstown NJ

Why wont they fit Magnum heads ? You dont have to use all the bolt holes … Just use 6 like the LAs.
unless there is another reason I am unaware of ?
I was told use this gasket:

Moroso 93050 Valve Cover Gasket Set, Fits Small Block Chrysler Mopar, 273-360 Non Magnum​