I'd spend some money on the heads, pre-'09 engines have a reputation for dropping valve seats if engine is overheated.
I'd go with the solid axle, believe it'll be lighter than the IRS on the Charger, and may be cheaper to narrow than IRS.
If you can't find a Jeep axle to use, look at an explorer, Durango, or Dakota. Probably have to narrow any of these choices.
A body rears are very narrow!
Your car will fly even with a stock 5.7, much lighter than that Charger, and Pursuit Chargers aren't aren't slow, I've got an '09!