That is refering to the 5th digit of the vin of the car, which is the engine code.
U=170 cid 6cyl
C=289 cid V8/2bbl
A=289 cid V8/4bbl
K=289 cid V8/4bbl/ high perfomance/271 HP(<---- That's a good one
F=260 cid V8/2bbl for cars built prior to sept. 64
F=302 cid/2bbl/ cars built after aug.67
J=302 cid V8/ 4bbl
X=390 cid V8/2bbl
S=390 cid V8/ 4bbl/ big block
R=428cid cobrajet/4bbl/ram air
Q=428 cid cobrajet/4bbl/non-ram air/begining aug. 68 ( 69 model car)
That's what that means. Hope that helps.