I have a 69 BU 12 14 G2 E and I can't find a reference that includes the 3894880NF casting code. The ring and pinion are correctly stamped for date and ratio.
Thanks
Are you positive it's not the 3894860? Often the cast 6 and 8s are very similar in appearance, where the top of the 6 looks like it is closed. See the picture in this old thread
http://www.camaros.org/forum/index.php?topic=7316.msg48359#msg48359
After careful scrutiny it is a 6, thanks it makes more sense now.