Figured that I would post up since I've been talking to a few pioneers on these builds
Basically, it doesn't matter if the car is an LX (300c, magnum, charger) or LC (New Challenger) platform.
The LX platforms and the LC are essentially the same with the exception that the LC has a shorter wheel base (smaller rear footwell area) and a few other small goodies that are related to it being a 2 door.
Typical wheel base conversion has a few inches removed from the floor pan and a few changes to the front fenders, primarily the center of the opening moved. This ensures that the front wheel is centered in the well, and the cowl/firewall basically remains intact.
Usually an older charger/challenger/road runner can be dropped on one of the floor pans with the addition of tubing going down the drivers and passenger door rail area. Tubing ranges from 2-5 inches. This fills in the gap and also creates a real strong area in the car.
Trackwidth on all of these modern cars is the same IIRC. Trackwidth is adjusted by running a different offset wheel, so not too bad.
Other info, old school gas filler is on passenger side. I initially wanted to keep mine on the passenger side. The tank cannot be flipped around to face the passenger side. It would be possible to snake the lines around, but realistically it far easier to just switch the filler port to the drivers side and run a modern Challenger flip top cap. These caps have the lettering going the correct way, where is if the passenger side old style was used the wording would be backwards.