It also helps that the Red Sox already have a left handed hitter who can hit 30+ homers and drive in 100+ runs -- Jacoby Ellsbury. Ells produced on an elite level in 2011 as a leadoff hitter, where he enjoyed the projection that having someone like Ortiz hit behind you provides.
Should Ellsbury move into the Ortiz's place in the batting order, the real test will be for Napoli. Will Napoli be enough of a threat to pitchers that they are willing to challenge Ellsbury? If so, Ellsbury would then receive a pitch selection similar to what a leadoff hitter gets (ie: more fastballs), and he'll have a better chance to reproduce his 2011 numbers. But, if Napoli isn't seen as a threatening slugger, all bets are off as pitchers will just pitch around Ellsbury instead of challenging him. Ellsbury certainly doesn't carry the same threatening presence and gravitas that Big Papi enjoys, so Napoli could really earn his contract money by providing that threat and letting Ellsbury benefit from it.
If Ellsbury takes Ortiz's place in the batting order, though, this creates another problem: Who will replace him in the leadoff spot, get on base and swipe bags to get into scoring position when Ellsbury comes to the plate?
Easy answer: If Jackie Bradley, Jr. ends spring training batting over .400 (he's hitting .519 right now), I don't see how you can't play him. No more of this "He's too young", no more "He hasn't had enough time in the minors", no more bullshit. JBJ is hot right now, making him a better option than any castoff veteran who can be brought in.
The Red Sox are not the Yankees, and they're not begging Chipper Jones to come out of retirement. The Sox have a decent options here and they should take advantage of them.