Fold down seats are a dime a dozen in Dodge Chargers, I'd check junk yards, forums, craigslist etc. to swap out your rears for fold down seats before attempting to cut any metal. I switched out my R/T seats for SRT ones and the R/T seats folded down. This was a while ago, I would've given them to you for free. I ended up tossing the R/T leather seats I had.
well its a 4th order the ported side is just under 4 and the sealed section is 2 so right around 5.7 or so with port and sub displacement
Okay I'm good then. I'm going with a 4th order firing through the arm rest for a single 12" Fi Q and it calls for 1.25 ft3 sealed and 2.0 ft3 ported so box will be around 3.25-3.5 ft3 total before displacements.