Junior Bradshaw and Kevin Liverpool were arrested in June near Stone's secluded house in the town of Cullompton, 175 miles (280 kilometers) southwest of London. Prosecutors have said a samurai sword and notes mentioning Stone's name were found in their car.
Exeter Crown Court heard Monday that results of a psychiatric test to determine Bradshaw's fitness to stand trial will be made available in June.
Bradshaw has not yet entered a plea to charges of conspiracy to murder and other crimes.
Liverpool has pleaded not guilty to the same charges.
