If your going to run 20's and bag it your going to have to do a Toyota clip up front with drop spindles or a Mustang II. Anything lower than a 20in wheel you can bag on I-Beams which there are full complete kits out there you can buy which will have right at everything you'll need. Suicidedoors has a good I-Beam kit if you want to go that route.
Pre 1997 Bag Bracket kit
http://www.suicidedoors.com/node/744