Ok. So this post is loaded with questions. But I will start off answering a few of them. The 46re never came behind a hemi. But the 45rfe did. And to match the two you just need to make a small cutout on the plate that goes between the engine and trans. As far as which engine is best, bigger the better right? But if you want the computers to be able to talk to each other, that's not the case. Unless you are going standalone or changing the entire dash out to a charger/challenger ect. A 2003 to 2005 ram. Or a 04-05 durango pcm and wiring will play nice with your electronics. But you will have to swap the cluster to an 01 to 04 dakota or 01 to 03 durango. Any ecu from the hemi cars or truck/suv 06 or later are a different bus system. They speak different languages... so best bet is any pre eagle, pre vvt motors. 03 to 08. When you get your ecu. Get the keys and skim. Shit I can go on for an hour on tips to go for and stay away from. Pm me. I will set ya down the correct path so that you aren't spending twice the $ for the same bs you can get the first time round in the junkyard.