Hello again to all. thanks for the accurate info. next question, (I know, what an idiot) what would be the results of putting 305 vortec heads on a 350 vortec motor? is it do able, is it to tight on the compression end of it and is the smaller intake valves that much of a hinderence to flow on a 350? a local dirt track racer and customer is moving and has kindly donated for the sum of ($20.00) a set of these heads. if nothing else I now have a full set of springs and rocker arms for a set of vortec heads. He informed me that the pocket next to the intake valve needs to be opened up a "little". but will work great. lots of power! I'm nervous. besides what do you use for an intake? thanks again...Stephen