Block Of Text I can Manage/Update Centrally For a Bunch of Posts

All blog posts will use same text and you can adjust it from one location. You mean this?

Not really. I'm trying have a section of text (text block) that I can insert into multiple posts but manage the contents of that text block centrally. That way if I need to update the text, I don't have to go back to every post and re-update them all. 

I can't place this in the footer, because (1) it will show on every blog post and (2) I need it in the middle of the post.

Putting blocks in the footer to be used in other locations is a common technique to do what you want. You then use CSS to hide bits in the footer and then some CSS and/or JavaScript to move things into place.

Please see Blocks Boilerplate.

Let us know how it goes.