Everything is possible, not all things are practical. Better to find the car with the type of tranny you want unless you have the money to pay someone to convert it or the knowledge and tools to do it yourself.
I converted an auto to manual in a Camaro- I know they are different, however the product from Hurst Driveline are straight forward and the support section is TOP KNOTCH! Am liked it so much I will do it again to my 73 Challenger from auto to manual. A big difference is that in the Challenge the Z-bar is welded to the frame, and the Tranny tunnel is much different, but they have a patch to fix it. IMO I say go for it, once done it is sure fun!!!
Joe
I did it in my old 67 Chevelle many years ago. It wasn't all that bad. In a Chevelle it can be done in a weekend if you have the right tools and know how. It looks to be a little more complicated in a Challenger but these days it seems like anything is possible if you have deep enough pockets.