If you want to keep the stock bolt pattern, you should look for the factory KH brake setup.(Kelsey Hayes) The system is not cheap though. The calipers will likely be seized and need to be rebuilt.

The earlier SB KH set up will work fine and maintain the bolt pattern not requiring a rear pattern or wheel change. Calipers can be purchased as well as the valve and lines, the spindles and hubs are not available to my knowledge and must be sourced from originals. Generally a complete set up can be bought anywhere from $250 up with rebuilt systems going for $500 plus pretty easy. If you go later BB pattern then you need the spindle out and the upper control arm from the donor car cause it takes a larger ball joint. You can still pick these up in boneyards depending on your area so not overly expensive and most every wearable part is available for purchase from the parts house. I have seen them go for anywhere from $50-250 depending on how complete and condition.