Yep you have a freeze plug back there.
No big deal replacing one. Knock the old one out, pop the new one in.
Time/money is getting to it. As the drive shafts, t case, trans, flywheel/flexplate have to come out first. Or pull the engine to do it.
97 Sahara, 74 Renegade, 72 CJ5, 55 Willy's (the Beast) Boss 302, 6:34 gearing, Bose 901 speakers.
God I miss that Jeep. Forgot the kinda Jeep, 80 SX4.