Before you roll your eyes

11 = engine = 170 1 bbl
5 = trans = automatic
R-1 = am radio
z-8 = buffed paint (silver)

b-4 = 564 = bucket seats

Looks like the "4" under the top "b" means bucket seats.

Valiant Signet, buffed silver metallic exterior with red bucket seat interior, 170 slant six with Torqueflite automatic trans, AM radio.

Kind of a strange combination - top of the line model, extra cost paint, red bucket seat interior, but with the smallest and least powerful motor available.