In 1969 I was working for Hughes Aircraft Company and they had a YF-12 (is that the same as A-12?)bailed to them to test the AIM-47 missile. I got to sit in the back seat (not fly, just look). NASA had a couple at the time and crashed one so they took the one Hughes had.
The YF-12 was an interceptor version. It was called the YF-12 to hide the still secret A-12 program.
The nose was modified with the chines trimmed back to allow fitting a radome, had a second seat (A-12 was single seat), and the camera bays were converted to carry missiles.
There were 3 made before the program was cancelled.
The sole remaining YF-12 is at the AF museum at Wright-Patterson AFB