Need help with rear disc brake conversion

My son and I are building a 70 Duster from ground up. Right now it is a body only. It had a slant 6 in it when I got it. rearend is a 7 1/4 I believe. not important because I bought an 8 3/4 today to go under it. The rearend is a small bolt pattern with 3:23 rears posi in a 741 case. I am looking to change the rearend to a big bolt pattern and I want to go with a disc brake setup. I know I need new axles but where do I go to get a disc brake setup for this. also what do I need. never done this before and I am in the dark here. thanks,Bill