I'm doing the same thing to an 86 2wd. The frames on the 2x's actually have a larger bump in the frame rail above where the axle mounts than a 4x IFS truck. So the 2x4 frames are actually more like a 4x from the early eighty's. For a tranny, look for a W56. If you are real lucky, and stumble across a turbo tranny, then go ahead and buy it as they are fairly strong, and fairly rare. Look for someone parting out an IFS rig, and buy the rear axle, tranny, t-case, E-Brake cable and set-up, and anything else you will want for doing the swap.