My opinion is with that many miles just add oil and drive it. Soon gaskets and seals will leak oil and the engine itself will wear out...oil pump, rings and the crank bushings.

When the engine dies, get a low mileage unit.

I did the valve seals on mine, $50 just for the valve cover gaskets, $100 for the tool, $30 for the stem seals.

A whole engine is $300-400. Just not worth all the expense and work in exchange for adding a little oil weekly.
1995 GM/LS -- 364K miles, engine rebuilt in my garage at 310K miles, 3rd plastic intake, 4th steering box, 2nd front suspension rebuild. MODS:1998 transmission, 1996 PCM, 1996 engine/trans wiring harness spliced in. A/C compressor cutoff dash switch, leather seats recovered with NOS cloth, dash switch for heater core shutoff valve. HPP springs installed front, police springs installed rear. 1997 steering box upgrade. My clearcoat is peeling off.

1992 Taurus LX -- 108k miles, added transmission cooler. Rear heavy duty springs.