Shoulder fire is a ridiculous concept, due to the fact that the recoil would be hitting you in the shoulder and functionally knocking you backwards. In the shield makes more sense.

That, or he could pull a Protector of Earth and abandon all reason to mount it in his chest.

I agree with the mounting on the shield, and even made a MOC of it, I am just worried that in a combat situation, a weapon would hit the missiles and would blow up the blaster and the shield.