What is the deal with this Rear End Housing?

[Cornpatch MO]

Went this morning. Took a look, the guy cleaned it up and thru some oil in it and it rotated nicely. All the gears looked in good shape and it had the 3.23 stampings.
Paid $450 and on my way.

Thanks to everyone for the help.

If the sure grip is good, I would say you got a good deal. Did you check for excess bearings play? That is the clutch type sure grip and all parts are available for it. I strongly recommend that you get a shop manual for the year of your car. You will learn the right way to do things...................MO

 

[Kern Dog]

The 3,23 ratio is a good compromise especially if your rear tire height is 27" or shorter. Most cars seemed to have rear gears under a 3.0 series, so the 3.23 is an improvement in acceleration ability. The higher the number, the more mechanical leverage the engine has for rapis acceleration.
You are fortunate that your car has that axle. I don't think I've ever seen a 73 B body with one since at that point, it was either the 8 1/4 or the 9 1/4 axle. I'd bet that your axle is a 71 or a 72 unit that someone swapped in long ago.
The term "Posi" is a popular mistake. Each of the automakers had some type of limited slip differential that they offered. Chevy called theirs "Posi-Traction" or POSI. It seems to be the most popular name although there are several others. Pontiac had Saf-T-Track, AMC had Twin Grip, Ford had a few including Traction Lok, Detroit Locker, etc. Sure Grip doesn't roll off the tongue like POSI, I wish that it did.

 

[Meangene83]

I have a sneaking suspicion the rear axel may have been from another car as well. Based on the castings numbers on the 383 heads... They read as 71/72 as well. So maybe they stripped a 71/72 for parts? Hence the heads and axel?

i love figuring this stuff out, it's like detective work for me. Finding out the history and lineage of the car.

Cornpatch. I did not check the rear end assembly for any of those mentioned things. I am not a mechanic nor am I mechanically inclined. I possess another trade skill.
i did look it over quite closely and spun the gear assembly while looking closely. It looked and felt right, sort of a gut instinct. I showed it briefly to my mechanic and he was impressed at the condition of the gears. He stated he is going to tear it down and put new 'this and that' into it. I said go to town, whatever your think.
i don't pretend to be an expert, I just pay those who are and stay out of the way.

i will have him check the items you mentioned though. Thanks for mentioning.