[JJchamp48]

This is the number I found on my diff: 3896838. Can anyone tell me what I have?
According to option plate I have a 4:11 rear end. I am switching to 3:42 and trying to make sure I need the new carrier, before I get it.

Also, on transmission this is #: 8THM097H. This is supposed to be original tranny and powerglide.
Casting # on housing: 8663548; # on tailpiece: 8642547-1.

Can't seem to find any #'s on tranny that is in truck now.

I have a 68 Shortbed step original engine was a 6 cyl, switched over to 350 and soon to be 327.