Is your Detroit a automatic or selectable locker? Actually it shouldn't matter either way. If it is a selectable it should act like an "open" carrier when dis-engaged. If it is an automatic locker; it should still allow the front to unlock. You shouldn't be having trouble with the auto hubs because D30's in YJs don't have hubs. All there is at the end is a unit bearing and an outer shaft. I replaced mine with a TJ shaft & don't have any problems. I wouldn't waste any money on putting manual hubs on a D30. For that price you could buy better axles & swap them in both front & rear.
1990 YJ 4" BDS lift, shackle reversal, 33" TSLs