I'd maybe try some 15W-40 or some 20W-50 and see what happens. If it's already that tired, probably ain't much gonna bring it back. Some folks around...
My Cars:
-1964 Comet 202 (116K Miles) - Awaiting Resurrection
-1987 Grand Marquis Colony Park LS (325K Miles) - April 2017 + September 2019 POTM Winner
-1997 Grand Marquis LS (222K Miles) - The Daily Workhorse & March 2015 + January 2019 POTM Winner