You might have more luck in an aviation sub. I've never seen anything like that from that time period. Looks to be a wind tunnel mock up.

It's Boeing Quietbird. Here's some discussion on Reddit and here's a thread on another forum with even a link to a patent concerning the project.

Boeing "Quiet Bird".
Only a mockup to test RCS.
You can see it was a wind-tunnel/radar test model due to the attachment device above it. It wasn't built with undercarriage.

Blueprint with Boeing designation 853-21
http://www.aerospaceprojectsreview.com/blog/wp-content/uploads/2014/12/2014-12-patreon-ad.jpg

US Patent file:
http://www.google.com/patents/US4924228

More info:
http://www.secretprojects.co.uk/forum/index.php?topic=8006.10;wap2 http://www.reddit.com/r/Military/comments/13mifx/the_army_had_a_stealth_jet_before_the_air_forces/

You may recognise the pedigree of this technology demonstrator in the Tacit Blue aircraft:
https://en.wikipedia.org/wiki/Northrop_Tacit_Blue#/media/File:Tacit_blue_side_runway.jpg

What it isn't is a YF-113G as suggested by others in some of those links.