I'm not even going to address the wiring issues (but they would be immense, not impossible, but immense).
The "HEMI" engined Crossfire has a completely different subframe from what I understand.
Somebody installed a small block Chevy into a XF once so I would think a small block Chrysler would probably fit. But if you're going to go to all that trouble, you might as well go with a 360 motor.
These cars are selling for rock bottom prices now, they make an excellent light weight platform for the back yard mechanic to play with. Small light weight "coupes" have always been desirable for decades. It wouldn't surprise me to see more "Hot Rod" Crossfires showing up as the years go by.
But plan on keeping it for a long time, I think it would probably be a little hard to sell.