SAN FRANCISCO - The Mets are going to have a different look when they return home July 26 from this 11-game road trip along the West Coast. Luis Castillo is expected to join the team Monday for the start of a three-game series in Arizona, Josh Thole likely will be demoted and Oliver Perez might even be added to the bullpen later this week as a $12-million "lefty-on-lefty" specialist.

That means dropping Ruben Tejada from the infield rotation, assuming Jose Reyes returns as scheduled Monday, and going back to the catching tandem of Rod Barajas and Henry Blanco despite their offensive struggles. As for where Perez gets squeezed in, that should cost Raul Valdes his spot in the bullpen.

"It's a challenge," manager Jerry Manuel said of the pending roster turnover. "That can be a problem because when you're in the process, you don't want to lose any ground. The process has to come very quickly."

Castillo has been on the DL since June 4 because of a bruised right heel and played in four rehab games for Class A St. Lucie, batting .154 (2-for-13) with a double and three walks.

Castillo likely will take the place of Justin Turner, who was rushed to the Mets from Triple-A Buffalo as an emergency infielder before Friday's game. Turner started at second base Sunday and batted second, going 1-for-5 with a double.

When Castillo returns, Manuel plans to hit him behind Reyes when Angel Pagan sits. Otherwise, Castillo will be in the No. 8 spot.

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"His on-base [percentage] is a big help," Manuel said. "His ability to see a lot of pitches. It's kind of something we've lacked."

Hisanori Takahashi remains penciled in to make his next start Thursday against the Dodgers in Los Angeles despite getting pummeled for six runs in 22/3 innings in Saturday's loss to the Giants. The Mets had the option of using Perez, who made his fifth rehab start Saturday for Triple-A Buffalo, but Manuel said they intend to use Perez as a "lefty-on-lefty" specialist when he returns - possibly later this week.

"Takahashi has struggled lately," Manuel said. "But he's pitched some big games for us and I don't think we're ready to pull that [switch] yet. Are we down on Ollie? I just think Ollie has to continue to find himself. I think Ollie could be of value for us in the pen."

The decision to send down Thole, probably after he catches R.A. Dickey Tuesday, seems to be the most difficult one. Thole has been more productive at the plate than the other two options; he's hitting .524 (11-for-21).

"When somebody goes down and can't do it, then Josh becomes a piece in that scenario," Manuel said. "But right now, it's got to be Rod and Henry."