I don't know about TJs, but with my YJ I did not have to put a BL in when I did the MML. I ended up putting the BL in later because of tire clearance issues.
I built my belly-up pan at the same time, but did have to drop it from the frame about an inch because of tub clearance issues. If you solely want to just get rid of the T-case drop and use the stock skidplate, then you should not have to do a BL.