To me, the most interesting thing about "midichlorians" of any kind existing in '77 is the fact that they were relegated to the trashcan along with the Kaibur crystal. And that young Lucas makes a point of saying that the force concept got better the less he explained it. And anything physical just made it mundane. It's impressive how all his instincts were so right on the money back then, even though he was fairly young and had only directed 3 movies. The Raiders story transcripts illustrate this very well.