A number of the guys on here have the burton covers. They sell them unpainted and fit realy well and have the clearance needed to fit roller rockers.
They only have one opening for the cap and not for the pcv(valve). If pcv is needed then an easy way to do this is get the pinto style cap which has a half inch take off to the side. Prise this apart and fit a pcv with a right angle outlet it fits nice and snug, then glue the cap together again. Ive been using it this way for years and its reliable and fuss free.