Can someone tell me if the "C" shaped bracket that attaches to the back of the spindle and connects to the tie rod end is common between disc and drum brakes on a 70 chevelle? I'm doing a drum to disc swap and was hoping not to change that part. Thanks.

They are the same. The set-up uses the same size bolts to hold it to the spindle. Actually drum spindles are the same as disc spindle except for the height of the center mounting hole boss.