ok not sure on your gauges but for your computer and trans I guess for lockup only, maybe more, you need your computer and wiring harness for sure. the computer is for the injectors and harness for the lockup on the torque converter.
The rest is pretty simple, you can leave your clutch pedal setup in if you want, but you'd have to push in the cluitch to start it(neutral safety) or wire it together, or to the brake pedal and change it to auto pedals etc. different options there.
for a shifter you can do a universal floor shifter or sorts, or swap steering columns out.
driveshaft may be a problem though, the ext. cab has a longer one but if the auto trans is longer or shorter then the manual one, it's gonna be off and need the right shaft, I'd bet the spline count is different regardless, a trip to the junkyard should find you the right one, just find an ext. cab with an auto and bam you're set.
The auto is gonna need a cooler, or you are gonna need to swap radaitors from your truck into the ext. cab. I would anyways going from a 4.3 to a v8, make sure it stays good and cool. v6's are sometimes smaller rad. core or sizes.
Motor mounts for the v6 truck need changed to fit in a v8, not sure what exactly gets done there.
