I purchased a MEI Mars AE 2631 D7 off ebay.com and received a D5 but everything worked fine.
I called Mars to ask them the difference between model number D7 and D5. The tech was very helpful and actually knew off the top of his head what the answer was. The D7 part denotes the bill stacker count at 700 bills, D5 500 bills. So games-people-play-and-more (the ebay seller) just did not give me the correct bill stacker but it was a really good deal at $160.