My B-body has the engine a lot further forward than a Duster. Ho0ks great with 10.5s, ladder bars and stock frame rails ( been 1.240). You existing drive train could net you 10.30s at 3000lbs. A little hop up to the existing engine and a careful weight saving program will get you there. Start cutting. Then start shopping . Lots of good used parts if you stay on it. Make a list and be ready to pounce when you find the right item. I second the Dana. If your 8 3/4 has 35 spine axles they may have enough spline to cut down and fit in the Dana. You'd be surprised how cheap you can build if you plan early and take your time to locate cheap parts. With a 2 year window you should have no issue.
Doug