Welcome to the forum. We have discussed this several times in the past, there are problems with the frame rails being in the way, and the alterations to make a Hemi work requires frame alteration (it's a width thing), and exhaust manifold location/dump problem. The amount of work would be very difficult, but not impossible, frustration levels would be very high, but I would love to see it done. So, until you actually do it and give us the pointers you had to do, the 360/5.9 is a good compromise. As far as the transmission goes, the 2.5/3.9 used a lighter duty 5spd, not sure about the automatic, beefiness, which would be something to look into, and remember, the 318/5.2 is internally balanced, 360/5.9 is external balanced and requires a matching torque converter/flywheel.