Spark plugs 1 and 2 look like the spark plugs that came out of my 1970 Plymouth, (180,000 miles) not good.
I have replaced valve seals on Toyota’s slant six (this engine is tilted with the rear bank facing the firewall). The usual complaint is oil smoke on start up, however your oil consuption is more than usual. Replacing the valve seals involves removing all four camshafts, not for the novice.
Perhaps the unintended example of why not to follow so many examples of “fleet” vehicles that have been reported to go 10,000 mile between oil changes.