with the advent of radial tires the 15x6.0" sized wheel was spec'd for use with them on the b-bodies (NO 15x7.0" Rallye wheels for 74 b-bodies)

the 15x6.0" chrome wheel had the W23 code - "chrome styled road wheels" (same as the 14" 5-spoke wheel)

the only item "inconsistent" is the TIRE LABEL, and it may be as simple as: that's the "minimum size required" with the 440 - is it still intact on the car? got a pic?