Challenger III - I actually printed out your picks to guide me, thank you for posting. In your pric's, it looks like you offset your floor cut by about 3/4 inch relative to your perimeter tracing based on scaling the photo.
The original hump I have (not sure what year or frankly if cuda or challenger, been 25 years since I liberated it with a cold chisel and hamer) seems to indicate about 1/2 inch offset along the centerline of the transmission while the other edges are about 3/4 inch. This based on the pattern of rust and overspray of undercoat.