I am checking to see if one can use blocks on a f250 or excursion with leafs in the front.

 

Its illegal, they cannot stand the lateral forces and would pop out.

 

RIght. You cannot use lift blocks up front. They are fine for the rear, but the added forces that steering puts on the blocks will/has caused them to spit out at the worse possible time. That's why they are illegal in most states.