Even though I have been taking old GMCs apart and putting them together for over 50 years, I still wind up with extra parts occasionally. The fact that I always have some parts trucks around to look at is helpful. You will actually be amazed that not that many parts fit in the wrong place. Occasionally you will discover you left out a part and have to take something apart again, but that happens. And at least you won't have rusted threads to deal with like you did on the first dis assembly. Good luck and have fun. The hobby was meant to be enjoyable...not something to worry about. You will get some real satisfaction out of doing something right and just laugh off the bloopers.