12:54 PM PT -- Burt was cast in Quentin Tarantino's Charles Manson film, "Once Upon a Time in Hollywood," but a source connected to the project tells us Burt hadn't shot his scenes yet.
He was supposed to shoot for 2 days, playing George Spahn ... the owner of the ranch where the Manson Family lived and plotted the Tate-LaBianca murders.
Burt Reynolds died of a heart attack Thursday morning at a hospital in Florida, according to multiple reports.
Reynolds was 82.
Burt was transported to a Florida hospital after going into cardiac arrest.