You'd be surprised at how little room those engine bays actualy have. My 48 Desoto is basicly the same car, but with a slightly shorter nose then the Chrysler. You would need to loose the inner fenders, and heavily modify the rad support area to make any those big Hemi's fit. Then there is the steering, would probably have to go rack and pinion, since the stock steering column would be in the LH valve cover.
These cars sem to fit a LA motor quite well though. A screaming stroker small block would be my choice.