Casting #3917123 is for 1968 Chevelle, 10-Bolt, 8.2” (12-Bolt Casting #3917124). The casting numbers may have either a prefix or suffix of "N" or "NF" they have no significance that I’m aware of. If you can find the numbers on the axle tube, I can get exact stuff, i.e: “XXMMDDP”

XX – ratio and type (standard, posi, metallic brakes, etc. – 47 different possibilities).

MMDD – Month and day of assembly

P – Assembly plant
• B = Buffalo New York
• G = Chevrolet Gear & Axle
• W = Warren Michigan
• K = McKinnon Industries