I'm working on swapping in a dana 300 with a twinstick. I'm using the flipkit and adapter ring (to attach the Dana 300 to the 6 speed tranny in my LJ) and cable shifters from NW Fab. The combo runs aroud 400 bucks. I also bought the LOMAX 4:1 gear set from JB Conversions. These gears are much stronger than the stock Dana gears and obviously have a lower crawl ratio. Just haven't gotten around to putting it on yet. From asking around I hear the week point will be the output shaft housing. the case it's self is cast so it's strong. FYI
Edit: I also recommend the JB Conversions Twin Stick Ball & Spring Kit, it helps prevent the Dana 300 from popping out of gear which I hear is pretty common.