Yep, my friends CJ had the same problem trying to get access to the rear valve cover bolt. It's a 1/4-20 bolt by the way.
He had a transfer case lowering kit installed so we had to remove the two bolts holding the trans mount to the cross member and jacked the the bottom end of the transfer case upward with a short 2x4 block of wood. Avoid lifting the transfer case up by the tail housing or you may damage it.
1984 CJ-7 Renegade