727 Build for Mid-10s

I know this is an old thread but it's valuable & pertinent. I'm getting ready in a couple weeks to tackle my trans, I have 3 trans to choose from.
I noticed that there are alot of clearances noted in the thread. What are the critical clearances ?
How do you figure out what is correct?
Should I measure my parts when I pull them out ?
I will pick up the books available to get a little grasp, mechanically speaking I'm capable, just need more info on the technical parts, since I will be replacing a few parts that could chop my foot off