You have everything you need for the swap. Now that I think about it, the existing wiring harness probably has at least the power run (and maybe the optical sensor) for the new ECM. But like I said, toss all of that. Pop the pins you need out of the existing truck harness. Put the ECM harness from the donor truck in there, connect power pins you removed that you need. You should be able to pop those pins out and into the new harness as if it came that way.. Forget that carb computer. Use the one from the parts truck. It's already set to run that motor. An yep, you can forget all of those stupid vacuum hoses. Run only what you need. The EFI systems use very few compared to the carb stuff. I despised all that junk on my truck too. Oh, don't worry about the optical sensor either. If your 85 has cruise, it's already there, and you can use it. If not, grab it off the parts truck. It will fit the old speedo head. Watch out for that tiny azz screw though. It is stupidly easy to drop, and you will NEVER find it. Your truck being CA emissions, it already has a CEL in the dash. My truck did not have one, but it had a place in the dash for it. I simply put a wire pin in that hole, ran it to the ECM and bam. There ya go. Course, you will need to run a fuel pump. I'd get a new one. It'll fit the old tank. However, there is one caveat here. The old tank senders are what they call "straight" tanks, and the electric pump tank senders are "cross over" tanks. You'll see what I mean. The fuel delivery line is the same, but the return and vent lines are reversed. Make sure that you connect the correct lines. I can't remember exactly if it's plug and play on that or not. Ignore that at your peril. You'll be pushing return fuel back into the vent, (blocking it) and possibly forcing fuel into the charcoal cannister. You will also need to mount your ALDL connector to interface with the computer. Don't worry. It's attached to the ECM already.
Don't worry. This isn't as hard as it seems. Just take your time. I didn't have a parts truck, so I had to run my EFI as a standalone harness which was more complicated than what you have to do. But removing the dash and trying to replace the harness to the fusebox isn't necessary at all. You will see in my thread where I had difficulty getting the truck started initially and my frustration.. This was due to me missing something basic. Had nothing to do with the install itself.
Since you have a parts vehicle, while you're at it, swap the belt systems too. Trust me you will be MUCH happier. Especially when you have to work on it. One belt. Buy a new idler pulley though. Ask me how I know! Almost burnt my truck to the ground. Confucious say, "Do not trust 30 year old bearing to not fly apart."