The team can make some paper moves to get under the cap with a 20 person roster. They can then put Savard on LTIR and sign Krug and Smith the first day of the season. But, the Savard LTIR money is still not enough to sign Krug and Smith, and you need a 13th forward and little cap cushion during the season, too.
They probably need to clear about 3 million in cap space from where they are now. Moving on from either McQuaid or Bart is a no brainer since there are 3 D for the 6 and 7 spots. You could move both, and rely on Warsofsky/Trotman/Morrow to act as your 7th D. Remember, since you need to still have a 7th D, let's say it's Warsofsky at 600k, you are only saving an additional 600k dealing both. Let's deal both.
That's 1.8 out of three. If you then move Campbell, and replace him with another 600k guy, you are looking at 2.8 out of the three, which is good enough.
If you can move Kelly, this all gets a lot easier, but his injury, longer term, age and NTC make that harder than some Bruins fan think. Moving something big like Boychuk doesn't need to happen unless it's a hockey deal to take care of the RW problem.