I apologize, yes a "late B" in my mind is anything after the 62-65 B's, and that is a wrong assumption on my part. My knowledge of anything after 72 is rather limited, and I might have steered you in a wrong direction because of that. So reader beware.
But my "theory" (?) still stands. grin

Regarding your thinking about being the only real crossmember in front of the K, yes, that's correct, but other then maybe aero loads, nothing is inputting forces into the chassis forward of the K, except the mass of the items in that area, bumper, brackets, headlights, etc.

Maybe an analogy, like trying to hold a muffler's weight and position by using a pipe hanger at the end of the tailpipe, rather then at the muffler?

Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.