What about the new Alpine R-W12D2? I'm considering doing one of those ported in my GTI next. The quoted depth is 7.25" which would give you just 1/2" for the pole piece to vent, lol. Not ideal but better than it up against the back wall of the enclosure.
I was going to try porting my current last gen type R 10, but I'm worried that I may destroy it in a ported situation since it is sealed right now.