new challenger trans swap

I doubt it'd fit in the trans. tunnel so you'd be looking at cutting the trans. tunnel and enlarging it and most likely highly modifying the crossmember. Then comes the electronics, you get to buy a computer to make that new trans. work cause everything nowadays is controlled by the puter. My guess is in the end you'd be much better off installing a Gear vendors cause the work involved in making a new trans. work is a lot and will most likely cost nearly the same as a gear vendors unit but require a lot more manual labor.

BTW: the only plus is a new bellhousing may not be needed when using a new Chally trans. I haven't verified it but have read they'll bolt up. But there is differences in the torque converter/flexplate so you may have to buy some sort of adapter or special converter.