Lots of modifications are needed for a v8 swap. The stock steering box is in the way of the exhaust manifold, requiring relocating a power steering box, commonly a bit to the left of the original position. There are kits available which require some welding to the frame. Next you will need to come up with a v8 engine mount bracket and a transmission mount bracket. Next you will need an open drive shaft rearend and and a drive shaft that fits. You will need to weld spring perches to your new rearend. I am absolutely certain that I am leaving out many more modifications needed. I see many AD v8 swap projects abandoned due to biting off more than one can chew.
A professionally rebuilt 54 235 with a highway-friendly rear gear ratio will give you plenty of the power and allow you to keep up with traffic on the highway without relining.
