At 23" front and 23.5" back with 215/70R14 tires all around. The front suspension is touching the bump stops slightly when it sits there. Drop spindles if you want to go lower. This seems to be as low as you can go and comfortably drive the car over speed bumps and such. I'm using flat leaf springs (XV) and Mancini lowering front hangers, you can probably go 23" in back if your careful.
I just realized you have a challenger and my info probably doesn't compare... assuming Cuda's and Challenger's have different fender lines. Oh well, sorry for the post.
-Dave