You should be able to call Airtran's reservation number, give them your flight number, and if they have a designated type of plane they will tell you. However, don't take this to heart as airlines tend to change equipment regularly based on plane availability. If the types of planes change, chances are your seating assignment will change, although AirTran doesn't allow you to pick your seats until 24 hours before your flight. I'd definitely take advantage of that.
Also, congrats on your pending nuptials. My first visit to WDW was also my honeymoon in 98. Make certain that you let everyone you meet up with that works with Disney that it is your honeymoon. I'm not guaranteeing it, but we did get some "freebies" at certain restaurants.
Have fun.