Former Tennessee transfer tight end McCallan Castles, wide receiver Ramel Keyton and tight end Jacob Warren are signing as undrafted free agents after not getting picked in the NFL Draft. Castles is signing with the Philadelphia Eagles, Warren is joining the New England Patriots and Keyton is headed to the Las Vegas Raiders. Castles caught 22 passes for 283 yards and five touchdowns last season, averaging 12.3 yards per catch and 21.8 yards per game. Keyton in five seasons at Tennessee caught 86 passes for 1,456 yards and 11 touchdowns. He had career highs with 35 catches for 642 yards and six…