I don't know the answer to your question, but I think the difference is in the dog bone thingamajiggers that keep the lifters from turning in a factory roller block...the non roller blocks don't have that so you must use lifters with tie bars on them....Also I could be wrong but didn't the factory roller engines have a step in the front of the cam for a retention plate? The BBC do...SO if that's the case a retrofit cam would be different in that regard.