Engine designation

Pull out a pushrod. If it's short, it's a roller.

But your doing a head gasket, that will require you to pull the intake, unless your really good. Once you have the intake off, the valley will have a spider holding the roller lifters inplace.

You need to get "LA" gaskets because they have an extra hole for oil flow that the Magnum engines do not.
Intake to head gaskets also differ.