Castro, in his first year of arbitration eligibility, made $496,000 last year, which was a bargain for a player who was named to the American League All-Star team, was a two-time AL Player of the Week and was named the team's Most Valuable Player. He could command more than $2 million this year.
Once the teams and the swap desired salary numbers for 2014, both sides can continue to negotiate to find a middle ground until an arbitration hearing is set next month. If they go to a hearing, a three-person panel would decide on either the team's offer or the player's desired figure.
The Astros could still pursue a long-term deal with Castro, though there has been interest in him on the trade market. Castro is coming into his own offensively, but there are concerns about his history of knee problems and his defense.
Guzman was acquired from the Padres in December in exchange for infielder Ryan Jackson. He will be given the opportunity to play first base and can play the outfield. The 29-year-old made $503,200 with the Padres last year, during which he played 126 games and hit .226 with 17 doubles, nine home runs and 35 RBIs.
He started at four different positions, including 33 games at first base, 25 in left field, three in right field and two at third base. He was especially effective as a pinch-hitter, hitting three home runs and leading the Majors with 14 RBIs in that role.
Brian McTaggart is a reporter for MLB.com and writes an MLBlog, Tag's Lines. Follow @brianmctaggart on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.