specifically because you're wanting to keep the stock 4" BP drums, i'd rebuild it stock.
problem solver upper bushings will likely give you more than enough castor in alignment.
disregard large ball joint parts for this project, to upgrade would mean changing out several other expensive and hard to find components-- to keep the 4" drums.
stay stock and keep it simple.
if your budget allows i'd upgrade t-bars, shocks and add a swaybar if you don't already have one.
