FINISHED! Here I have restored the Blackbird to it's original dull black/nearly a very dark gray color. The Future had really darkened it, and subsequent coats of Mr. Topcoat Flat just was not bringing it back to its original Tamiya XF-69, Nato Black.

Here is a quick and informative video on the plane:
https://www.youtube.com/watch?v=81ofbypM2aI

Here is a link to the interesting and informative video of a pilot's lecture on the SR-71 I referenced here, in which he discusses his experiences with piloting the Blackbird, visiting Area 51, etc:
https://www.youtube.com/watch?v=mHjhgeyhuKk

Here is a fascinating documentary on this plane:
https://www.youtube.com/watch?v=s3tvBRs8_qU

....And another:
https://www.youtube.com/watch?v=OBVmYi7mkZM

And the Blackbird's family of planes (there were more than just the SR-71!
https://www.youtube.com/watch?v=S2xgI3wQbWQ