I'm also a little bit confused about how you sideboard against Gifts. Why on earth would you sideboard out Necropotence? Just in case they resolve their entire combo and only have to attack you for 22 as opposed to... 22? I'm not sure I understand your justification. I would think that Necropotence would excel in this match because they tend not to touch your life-total until they are about to win.
I´d totally agree with you on that. During testing against Meandeck-Gifts I realized that I could win most of the games only if I had been able to resolve an early bomb - and Necro is definitely one of these. Once I can resolve an early Necro it will most likely win me the game - Meandeck Gifts is no exception for that. Thus, I can absolutely find no reason why Necro should leave the MB in this match.
Whereas DSC is just horrible to have MB against Gifts. In one of the first games that I played against Gifts, I made the mistake of tinkering for DSC instead of Jar. Since Gifts runs 4 Merchant Scroll, 3 Tutor + Gifts+ Fact+ Brainstorm, they will always find their Echoing Truth or Rebuild and bounce your Colossus back to hand. So unless I can go Tinker+Walk, I´d always go the Jar route.