From the US Treasury FAQ:
"Both United States Notes and Federal Reserve Notes are parts of our national currency and both are legal tender. They circulate as money in the same way. However, the issuing authority for them comes from different statutes. United States Notes were redeemable in gold until 1933, when the United States abandoned the gold standard. Since then, both currencies have served essentially the same purpose, and have had the same value. Because United States Notes serve no function that is not already adequately served by Federal Reserve Notes, their issuance was discontinued, and none have been placed in to circulation since January 21, 1971."

You are correct the BEP prints all money, but it is done solely at the request of the Fed, as described in Section 16 of the Federal Reserve Act. There are many who feel that this is unconstitutional, but it has never (to my knowledge) been challenged. Even if it has been challenged, obviously it wasn't successful.

You are also correct that congress could bring in an alternative to the Fed at any time, but I really don't see that happening. They are to invested in it at this point.

Anyway, none of this is meant to detract from your post, which was great.

Kevin