My rear axle

Hi everyone!

As I am a newbie to Mopar, I was researching the running gear fitted to my 63 Dart HT. Originally (obviously) a /6 it has been retrofitted with a 318/904tf combo, with a rear axle which appears to be an 8.1/4". (Source:"mopar axle spotters guide" available via Google)

Surfing the forum, I can find virtually NO mention of this axle? with many references to either the weak 7 1/4, or the bullet proof but rare (in A body form) 8 3/4.

Can you Guys shed any light on this for me?

Regards
Rob in the UK
Most 73up 340/360 cars came stock with 8 1/4 s.g rears.Also I,ve read about the 8 1/4 coming in earlier B-bodies.