wellgeo03, if you have 9 leaf packs, they will be 2600lbs to 3800lbs, 10 leaf packs are 4000lbs up. there's 4 or 5 standard ratings for rear k30's. check out Standens springs, their out of alberta, good quality & prices. the heavier springs are only a few dollars more-imo there's nothing wrong with overkill!
one thing you might want to check when running air bags is frame twist where they mount. heavy loads on the bags will bend the frame rails inward. mine were bent in a 1/4" on each side, straiten them out & install a crossmember there. i used a piece of 1/4" angle
pretty basic, but cheap, strong & reliable. stock springs with flips & blocks & bags to get rid of the tail dragger look when loaded, with extra cross member
