I've heard that the Napa 12069 is not an actual quad ring, just a regular o-ring. It will probably be fine. I've used o-rings there before. Just make sure not to overfill the trans. The kickdown ring is not meant to hold pressure from a high fluid level.
The valve body is held up by 8 or 9 (depends on year) bolts. The bolts will have either 3/8" or 7/16" heads. Do not remove any bolts with 5/16" heads. The whole thing will come out in one piece. Afterward you can disassemble the shift linkage to get to the seal.
The difficult part is going to be installing the valve body and getting the internal shift linkage and kickdown lined up. You'll have to pull the kickdown lever into place just as the valve body is being seated. You should feel the spring tension of the valve against it. At the same time you need to make sure the manual valve gets positioned correctly on the shift peg. It will probably take a couple tries. Once you think everything is correct put 2 bolts in to hold the valve body in place and test the shift linkage. You should feel all 6 positions and see the manual valve moving at the rear of the valve body. If this is wrong take it back off and try again. It almost takes 3 hands and the dripping trans fluid doesn't help any.