Rear Main Seal

Yes. It is easy once the oil pan is off. That part is not easy, but you don't need a lift. You will probably need to unbolt at least one engine mount and lift the engine about 1" more above the K-frame to get at all the bolts and work the pan out. You also need to disconnect the Pitman arm, which requires a special tool (cheap at Harbor Freight). The rear seal is in an aluminum holder. If any of the tapped holes for the oil pan bolts were stripped (common by gomer mechanics), now is the time to repair the threads (Heli-coil). The rear seal is the same PN as for the Hemi engine! The seal is a 2 semi-circle rubber piece. You can push the upper half around to get it off the crankshaft.

True that most early U.S. engines can have the rear seal changed w/ engine in car. Some had a rope graphite seal, but they make a grabber tool to pull those out and new rubber replacements. My 1985 M-B diesel was designed mean. It has a rope seal, but they put a locking pin in the block so you can't pull it out without lowering the crank a bit. New engines (~1995+) have a 1-piece seal which bolts on the rear of the block, going over the rear crankshaft. You must remove the transmission to replace those.