The Crane kit uses individual cast guides with a nylon insert instead of a more conventional guide plate for the push rods. These are quite thick holding the bottom of the stud up almost 1/8" higher. This can result in the bottom of the rocker contacting the base of the stud.
Hughes has a more conventional guide plate and stud kit that I would recomend over the Crane kit.
Also, you need to check the contact of the roller with the top of the valve stem. Not all Chevy rockers are exactly the same and you can run into issues where the roller will run off the side of the valve stem. This can be adjusted with different length push rods but you need to check and likely get custom length push rods.
FWIW, if you are not pushing the engine past 6000 rpm there really is no reason to not use the factory magnum stamped rockers.