What Rear is this?
 

I will admit. I know nothing about rear axles.
This came with the car I am currently restoring.
I highly doubt its the original axle since there is no visible code and the PHS says
this car had a standard 2:73 Rear
I am assuming this rear now is a 3:55
I spun the rear drum 1 revolution and the pinion spun a tad over 3.5.the carrier?
I dont know if its a limited slip or not. Anyway you can tell by
Housing is Casting # is 9788347
I cant find any info online with this casting number

It’s a limited slip diff, just by looking at it I can see that. If you turn the pinion flange and both rear axles turn the same direction you definitely know it’s a posi rear even with the cover still on.

The gear ratio can also be determined by looking at the numbers stamped in the ring gear and doing some simple division.

and it aint a freeway 256 gear with those big ring gear teeth ....

I found the code on the axle tube
Its ZH which means its either a 1965 or a 1968 3;55 Nodular Iron 4 pinion design
Is there anyway to tell the difference from a 1965 and a 1968 rear?
are the overall dimensions the same or different on both years?

65 is narrower, but for an even easier ID look at the spring perch. 66 and earlier had a flat surface, spring was bolted on with a retainer. 67 and later used an inverted pocket to locate the spring (no bolt)

thanks..
of course! I knew that but didnt even think of that.
must be a 68 rear then
So the length and dimensions are the same then?

The ‘68 rear is 1” wider overall compared to a ‘65 rear.

Thanks for that info
I have a 67 so this rear should be same dimensions then.
I been reading that 4 pinion rears are heavier duty too over the limited slip with springs in the carrier
Any truth to this?

4 pinion gears are stronger than 2.
And, there is preload springs in the 4 pinion units too.
Nice find, BTW.