The Indianapolis Colts are working diligently to lock down two cornerstones before training camp ends.
"There is optimism that they could finish both extensions before training camp ends," Rapoport said. "Once camp ends, then business starts and it's no more time to talk contracts."
After some offseason speculation that Indy drafted rookie receiver Phillip Dorsett to eventually replace Hilton, the sides mutually want to strike a long-term solution.
"This organization loves and wants to reward (Hilton)," said Rapoport. "He's a high-character guy and they want nothing more than to give him the kind of contract extension that he deserves."
Hilton's agent Drew Rosenhaus was at Colts camp and is expected to meet with the team's brass Tuesday.
As for Castonzo, the former No. 22 overall pick in 2011 is set to make $7.438 million. Pro Football Focus ranked the 26-year-old blocker the No. 10-rated left tackle in the NFL in 2014.