Joshua
You are asking the same question that many of us have asked, and as you have seen there are many answers. The 350 SBC swap has been done so many times that its almost a cliche. Even considered boring. But it works; that engine series is plentiful with easily available parts and tremendous support in the aftermarket. Its good, cheap power. The traditional wisdom says there will be steering issues to address because of the AD trucks narrow frame. But commenting on 52Dave3600's comments: my other
50 3600 had a 307 V8 in it when I got it. Whoever did the swap moved the steering box out about 1-1.5" by fabricating an adapter/bracket. The exhaust manifold on the driver side exited at the very rear at about a 45 deg angle and the one on the other side dumped straight down right under the rear spark plug. The motor side-mounts were home-made. The bellhousing had the mounting flanges and rested on the crossmember. Behind that the truck was stock; SM420 with front enclosed drive shaft, and all.
You are doing right by gathering all the info you can and making a plan before you start. Good luck!!
