A major league source has confirmed that the Red Sox have traded outfielder Josh Reddick, first baseman Miles Head and right-hander Raul Alcantara to the A’s for closer Andrew Bailey and outfielder Ryan Sweeney. A few quick reactions to the trade:

1) The Red Sox have built a solid back-end of their bullpen, with further reinforcements such as Ryan Madson unlikely. Both Andrew Bailey and Mark Melancon, along with — in all likelihood — either Daniel Bard or Alfredo Aceves (one of whom is likely to end up in the rotation, the other in the bullpen) and Bobby Jenks (whom the Sox expect to have back) creates late-innings depth, particularly if Matt Albers and/or Felix Doubront and/or Franklin Morales can further lengthen the group.

The Sox have seen Bailey — a two-time All-Star — show the kind of stuff to be one of the elite closers in the American League. He’ll almost surely be the end-of-game option for the Sox as well. Though there have been health questions about him in recent seasons, the other pitchers with closing experience and/or potential (Melancon, Jenks, Bard/Aceves) permits the Sox to be insulated (at least on paper) should he be sidelined.

2) The Sox still have money to spend. They won’t be spending a ton, but in adding Melancon and Bailey through trades, the Sox acquired two solid late-innings arms who will cost less than a third of Jonathan Papelbon next season. As such, the team still has some money to either sign or trade for a starter. That will be their primary offseason need going forward.

3) In exchanging Reddick for Sweeney, the Sox parted with a major league outfielder with upside in Reddick in exchange for a player whose on-base skills and ability to play all three outfield positions will fit into the club’s short-term needs. Right now, Sweeney and Darnell McDonald wouild be the Sox’ right field combination, though the Sox are still looking at right-handed outfield bats. Regardless, the Sox were likely going to get to a point where they had to trade either Reddick or Ryan Kalish at some point given the potential positional redundancy of the two. In a best-case scenario for the Sox, Kalish would be ready to be an everyday big league outfielder by the middle of 2012. Reddick would have been that for them right now, but the upgrade to Bailey with the anticipated availability of Kalish in the not-too-distant future made this deal feasible.

Sweeney, a former second-round pick, is a career .283/.342/.378/.720 hitter. The Sox believe that his swing and approach will both play well at Fenway Park.

4) Alcantara was the clear second component of the deal. When the Sox were scared away from the Rich Harden trade this summer, it was because they couldn’t stomach the prospect of losing Alcantara as the second piece in the deal.

It’s almost impossible to say what the 19-year-old will be. He’s a relatively raw right-hander with a big arm. He dominated in the Gulf Coast League (0.75 ERA in 48 innings) and faced adversity after a mid-year promotion to Lowell (6.23 ERA in 17 1/3 innings). His fastball/breaking ball combination suggest at least long-term big league bullpen potential, and he has the upside of a starter. Still, he’s likely at least five years from a regular job in the majors, and there’s immense uncertainty about his future. That being the case, he’s precisely the type of player for whom the A’s (whose visions of contention are entirely driven by the long term) should deal, and the type of player for whom the Sox cannot sabotage a deal.

5) Head made a significant jump in his prospect status this year by producing a dominant stretch with Single-A Greenville and then holding his own as a younger player in the Carolina League with High-A Salem. He doesn’t wow anyone with his physique or athleticism (he would be an atypical success story, having to follow a path of someone like a Billy Butler), but the 26th rounder (who signed for $335,000 in 2009) has always left the Sox convinced he can hit.

The first baseman garnered little attention in the Sox’ system while hitting .240/.328/.341/.669 with one homer in Short-Season Lowell in 2010. But in Greenville this year, Head asserted himself in a way that ensured he could no longer be overlooked.

The 20-year-old earned a promotion to Hi-A Salem in late-June after leading the South Atlantic League in average (.338), slugging (.612), OPS (1.022) and extra-base hits (41 in 66 games). His consistent results reflect both improved conditioning as well as an improved mental approach to the game.

“Last year, I was getting myself out chasing pitches or swinging at maybe not a hitter’s pitch in a hitter’s count,” said Head. “This year, I’ve figured out my approach and stuck with it.”

Still, Head was never going to leapfrog Adrian Gonzalez as the first baseman of the future, so he represented a moveable piece. He hit .254/.328/.405/.733 with seven homers in 63 games with the Salem Sox.