The main difference is that the nomeclature just changed. The AAV7A1 received a new upgunned cupola and some other inprovements, but they are essentially the same vehicle. Later ones received the suspension that is used on the Bradley so they sit higher. There is also additional armor added to later vehicles.
There are some photoetched sets available. There are also some individual tracks available. There is an older style and newer style (called "bigfoot" in the modeling world). The difference being the old style has triangular shaped pads and the new stlye are rectangular.
Unfortunately, no one makes an interior. The kit is so cavernous that it just begs for an interior.