70 duster 8 3/4 conversion to 4.5 drum or disk hardware

Thanks guys, lots of great information here, but now I have to ask another noobie question. What do you mean by the standard Mopar offset, and not the A-body offset? And sorry for the link not working http://www.classicindustries.com/mopar/a-body-duster/parts/mm3042.html