1957 DeSoto 8 3/4"

That is a good idea.

Alright one last question as of now anyways. I'm using 1965 C-body housing and axle shaft and the 1957 DeSoto center section. It looks like the thrust block in the differential is different width or the 1965 axle shafts are slightly longer compared to the DeSoto axle shafts. So could I cut a little off the axle shafts or is there a different thrust block to put in the differential? How much clearence should there be between the axle shafts and the thrust block?

To clarify. This 65 cbody housing is flange with the 5 bolt holes? You’re using the correct backing plates and axles that came with it. If so, you shouldn’t need to change anything. Just put the chunk in.