MK3 & Atlas

I have an rs inlet rocker that has been damaged because the motor was run with out oil. I cannot pass the spindle through it. I have a replacement from an atlas head, just checking on whether or not it is interchangeable or not. I can read the same part number...067....on both. The MK3 looks like it is beefier than the Atlas rocker but is that all important? Same cam...same springs... Is there a ratio difference?

Depends on the year/engine # of Atlas engine....changed late '65, ser # 114870.

Mike B