Cylinder heads

I am in the process of making a deal on a 71 GTO, and in doing a little research, it looks like the power rating took a significant drop in that year compared to the 70 Ram Airs. I am sure that they dropped the compression ratio, but wondered if anyone could tell me if the combustion chambers are larger on the 71 heads? did they breath better in 1970? Did the just put dished pistons in the 71's? How about camshaft differences? Also, I plan to use a 70 Header panel and hood on the car, and would like to know: Are the fenders any different? are the header panels and the front valances, two seperate pieces? Thanks for any help.