That looks a bit smaller than I expected, from my uninformed opinion. Maybe it's just the angle of the photos.

How did it fly for 10hrs (based on the parent article) at high speeds without a ton of space for fuel?

Lots of aerial refueling. 10 hours in the air, yes, but not on a single tank of fuel.

"The SR-71 needed to be able to fix its position within 1,885 feet (575 m) and within 300 ft (91 m) of the center of its flight path while traveling at high speeds for up to ten hours in the air."

They refueled in-flight, and the high speeds they are referring to probably weren't sustained for 10 hours... I think it is more like "while traveling at high speeds and for up to ten hours"...

The SR-71 is smaller than you'd think ([edit] to my eyeballs, at least).

As far as fuel goes (a) in a three-dimensional object, "volume adds up fast," and (b) aerial refueling.

(p.s. My dad was a US Navy pilot in the early 60s when celestial navigation was still core curricula.)

The A-12 was the original single seat version developed for the CIA. But eventually the Air-Force was given all responsibility over the planes and they re-designated the plane and added a second seat to fit their pilot philosophy.

There were supposed to be more variants, even tactical bombers but military politics and budget constraints and yadda yadda yadda.

The Air Force museum in Dayton has a YF-12, which was the prototype of the interceptor variant. It's readily distinguishable from the A-12 and SR-71 because the chines don't extend to the front of the nose. This so that the nose cone could be made of material that is transparent to radar.