Hard to tell, but since there is no "O" axle your's must be "C" or "D". The little ears on the left side of the letter in your pic lead me to say "D". Fairly easy to count the driveshaft revs/wheel rev to determine ratio.
What else doesn't match? A 63B is a Fairlane 500 2-door hdtp, bench seat.
Heres a closeup of the door tag and the numbers from the build sheet. It still looks like a 0 too me. I ran the number in another decoder and it said it was a Fastback 500(bucket seats) I'm trying to find the decoder again and give ya a link.
In my book the letter "O" was used in 1967. There were two ratios with this code: 1 was 2.70 and the other was 3.10. It was also used in 1968 & 1969 with a ratio of 2.50. This in the catalog issued by Dearborn Classic.
If this is wrong I will dig out my 1967 Fairlane Shop Manual by FOMOCO.
<font size=-1>[ This Message was edited by: rayell on 4/6/06 7:14am ]</font>
It is a non locking rearend. See if you have a tag on the rear end. That will give you the ratio. If not you will have to turn the rear tire one turn, and see how many times the driveshaft turns. This will give you a guestimate.