Difference between the 2 80mm Pro'M & homemade CAI

What is the difference between the "short" and "long" Pro-M 80mm MAF's, and do they go for the same price? Also, if I wanted to make my own CAI kit for the 80mm MAF, how would I go about it? Does anyone have a good setup that they've built from either PVC or some other material that they can give me pics of or directions on how you did it?

Is there better airflow between the 2 meters though? I don't understand why there would be 2 different ones if they both flow the same and are the same price.