The Dodge Challenger Message Board

I'm trying to locate a set of 70 big block valve covers. Does anyone know how to distinguish those of a 70 383/440 from say a 69 or 71 model year? I cannot find a part number stamped in any cover I've looked at either. I think the 70 has holes for a gas gap and breather on one cover and a pcv valve on the other, but I know there are some subtle differences between years and perhaps between engines (383/440magnum vs. 440/6). Any info would be appreciated.