Plain and simple
When you are looking at the head , on the two top corners just at the outside of the valve covers, there will be a #4 or a #2. Seeing this will tell you what kind of heads you have. Now you will not know if they are open or close chamber heads unless you pull the heads. Ok, if you dont have a #4 or a #2 on there, the heads are off of a 351M or a 400.