The
B1A/B approached a blended wing, although 1) the blending was interrupted at about 15% span by the need for variable sweep, and 2) it is a fair question what is "blending" and what is just an oversized fairing. Definitely not a flying wing, though. But, of course, that was Rockwell, not Boeing. However, Rockwell Aerospace is now a part of Boeing.
https://upload.wikimedia.org/wikipedia/commons/c/c8/A_B-1_Lancer_performs_a_fly-by_during_a_firepower_demonstration.jpg