I cant give u any reviews on a 6.4, but i can tell u these things are HD... top quility for everything PMF makes. The finish isnt that great, but i have the old style. I bought them off a guy who had a 6.4 and loved them, he was returning it to stock and trading the truck in. I did re powder coat the blocks but like i said they are pretty old, the ones i have were his first designs. They are pictured in my sig.
If u are looking to buy a set with 5.5" blocks... im open to to trades. The bars are great for what they are and are great on a SD since the bodys sit lower on the frame. Im not a huge fan of they way they look on my truck. I may go with cal-traks just for the more hidden look. But that is if you are close to me as shipping would be crazy