I just finished installing a one piece AMD pan. These are my thoughts.
Fit-pretty good/great. The area at the back at the bumper support where the frame has the bumper support tapered brackets was a little high compared to the frame rails. This could be specific to my build since I mini-tubbed the car and had to alter the pan to fit around the stretched wheel tubs.
Thickness-yes AMD is thick. I though this was a quality feature! Thick is good in my opinion!
Overall-great
If I did it again I would buy the two piece instead of one piece. I am not doing a numbers matching type resto. Mine is a full pro-touring modification build so I wouldn't care about the seam. It will be covered in DynaMat and other items. The 1-piece is a pain to get in and if I didn't have a quarter removed I'm not sure I could have gotten it into my car. It was a PAIN!
Do not plan on putting a 1-piece in without a little cussing and beer drinking
Wes