Disc brake conversion regarding lower ball joints

I have a set of single piston discs from a 75 Dart to put on my 70 Dart originally with 10" drums. I pulled the upper control arms, rotors, calipers, brake hoses, and lower ball joints just came with the setup when I pulled it. I was told I could use my original lower ball joints, but that I just needed to convert my upper control arms (with bigger ball joint) to make this setup work. Well, the holes and bolts on my lower ball joints are smaller than the ones on the spindle of the discs, so I obviously have to change the ball joints to be the ones that came with the discs, but the arms are shorter and hang lower than my original ones. Is this going to affect the way my steering linkage hooks up to them, or my steering at all? I'm confused.. I was told my lower ball joints would work.