What they have done is actually quite simple, they made valve guides that fit properly, are easier to install, and shaped to help air flow instead of just copying the OEM design. The GSC Power-Division valve guides are made from true C67410 Manganese Bronze and turned on a dedicated precision CNC turning center. What this means for you and your installer is less time fitting guides to the head due to holding the tightest tolerances in the industry with the best quality control possible. 

Quantity: 8

The stopper style is simply what it says. It has a stop integrated into it so that it wont get pushed in to far. Most machine shops have to drive and check multiple times to get the proper protrusion, these have it built in.