Chevy 12-bolt identification

[GotGrunt]

Originally Posted by John Brown

I'm not a Buick expert but here's what Hemmings has to say about 12 bolt Chevy axles in Buick Stage cars in 1970.

https://www.hemmings.com/magazine/1970-Buick-GS-455-Stage-1

What to watch for: GS 455 Stage 1s were automatically equipped with reinforced upper control arms that were not available on the base GS 455. Furthermore, Canadian-built GS 455 and GS 455 Stage 1 cars were furnished with Chevy's 12-bolt differential; however, it featured Buick casting numbers rather than Chevrolet's. A Space-Saver spare became available for the first time.

Interesting, I did not know that. Do any documented examples exist? What is the Buick casting number for the Chevy 12-bolt?

Originally Posted by Baron Von Zeppelin

70 Grand Prix 455 also used 12bolt rears.

Is it for sure a 2.73 ratio as Bentley mentioned ?

It very well may be out of a Grand Prix 455. From what I’ve read, the GTO/GP 455 12-bolt ratios were limited to 3.07, 3.31, & 3.55. The LE code (2.73) listed for the GTO/GP is for the 10-bolt. That is where the confusion is. It is for sure a Chevy 12-bolt and it is definitely stamped LE.