One of the things that makes a good handling car is 50/50 weight distribution. Consider that the baddest muscle cars were nearly undriveable in anything but a straight line (including old big-block Vettes), but smaller engined versions of the same cars did quite well for their day. Also consider that great pains are often taken to maintain a good fore/aft weight balance in modern sports cars (rear transaxles in the Porsche 928/944/964 as an example). Dropping in a heavier engine will detract from your Crossfire's handling.

Then again, who says the HEMI (5.7L or 6.1L) is heavier? It is hard to judge an engine's weight solely on displacement. Consider that a Porsche 911 engine (one of the old air cooled types) weighed more than a Chevrolet 350 V8. I know that's probably not the best example, as air-cooled motors obviously weigh more than water-cooled ones (any sports bike fanatic knows this). However, looking at that 3.2L V6 in our engine bay, that's a lot of metal. OHC engines require additional cams, larger heads to accommodate them, etc. A pushrod engine can be quite compact, as there is just one cam nestled deep in the block, the heads can be smaller, etc. It would be interesting to see a weight comparison between a modern HEMI and this benz motor.