This ^^^^^^ is NOT correct information. After 8 years, we should know better.
Every 2004 MM is a 300A. There was only one job series in 2004 unlike the switch from 2003 300A to 2003 300B where the changes in features were made to remove the dash clock, change the fuel door release, swap out the full size spare, etc. The 300A vs. 300B distinction only makes sense when talking about the '03 MM.
It just so happens that the 2004 MM ended up with the same features as the 2003 300B model .... plus the beefed up transmission and the dual knock sensors.
Since DTRs were only available in 2004 .... they are all 300A. Check your window sticker.