One of the ways to negate the 2.5" difference is to remember the Charger uses a Front wheel drive offset wheel so the center hub is pushed out in relationship to the wheel center.
These rear ends are weak to say the least but the main issue is in the axles. There are two gear choices for the SRT and R/T rear end you can have the stock 3.06 (SRT) or 2.82 (R/T) But Richmond sells 3.23 and 3.55 gears for these 2 carriers.
If you need some more info on these rear ends I build a ton of the new Hemi's give me a shout.
