Help with Rear Axle Housing

[SD69C10]

I purchased a rear disc brake kit from MPB and was trying to install it this weekend. The rear end axle housing currently on my 1969 C10 is what's in the picture and has a 12 bolt main. The instructions show that I should have a 4 bolt flange. Can anyone help me with what I have so I can try and track down the correct kit?

[Accelo]

You may have a transplanted housing. Am I correct in saying the brake backing plate is welded to the housing? May be you have a correct kit and an incorrect differential housing. How about a picture of the differential? May help sort this out.

[SD69C10]

Thank you @accelo....yep after doing some research it looks like I have a 12 bolt from a 63 C10. The info I found was that year was the only year the backing plate was press fit on.

[BigBird05]

You should be able to read the axle code from the bottom or front of the RH axle tube. That would tell you the year and gear ratio.