Two immediate changes stand out, which may or may not answer your question:
1) McClain would immediately plug in at MLB, allowing Hitchens to slide over to the spot vacated by Lee (grumble grumble). Once Lee returns, a linebacking corps of Lee/McClain/Hitchens sounds a metric fuckton better than Wilbur/Hitchens/Wilson - which was the three linebackers on the field on the final play last night. Gachkar can move back to a depth role which is better-suited for him, Wilbur can go back to being a pass rushing specialist and Wilson can go back to learning where the fuck he's supposed to be while stapled to the bench.
2) Hardy would allow Tyrone Crawford to move back inside in obvious passing situations. I saw him lined up outside a few times last night, which made for a very ineffectual pass rush what with Lawrence struggling all night to beat the hobbled Armstead. The other benefit is it would allow Lawrence to move over to the left side of the line, giving him the opportunity to go against the lesser right tackles of the world.
The addition of both players should also help the run defense because that is an area where McClain excels and Hardy would allow Hayden and Crawford to focus more on taking up blockers, rather than trying to add to the nonexistent pass rush. They also give the front 7 more depth for rotation, which will be even more critical up against the fast-paced offenses they'll face, like New England, Philly and Green Bay.
Unfortunately, I can't really speak to the scheme. I don't know where Hardy would fit in, since he's new to the team, and I'm not that schooled in football (luckily, our friends at ITP could probably help). I like to pretend I know what I'm talking about but I never played organized football, so the X's and O's are still somewhat outside of my area of expertise.