Cracked lower control arm is really bad. Do not weld it. No, the bushings couldn't have done that. Get SS conversion lines from
http://www.pdm-racing.com or ProjectSilvia.com. They are the proper fitting. You first post is erroneous. The conversion lines are the proper sized fitting so that you done need an extra washer. If you but conversion lines for your S14 they will work. Stock lines CAN work with a washer but are not recommended. Stock Z32 lines will work as well.