If you want to run a 3-4 I would do something like this..
Leave the dline alone
OLBS - Harper and Dunbar
MLBS - Vilma and M. Mitchell (whichever is the fast Mitchell)
FS - Sharper
SS - Jenkins
CBS - Greer, Porter, Robinson, Young
I think Greer does an adequate job at cb, but if he's not working out for you you could move Porter up to #1 and Greer to #2 or if you don't want Greer in at all put Robinson at #2.. bring Sharper in at FS and Jenkins in at SS, if Sharper is too slow for your liking you can put Usama Young in at FS and I find that he is a pretty good player to user.. You want to bring Harper from SS to OLB, because he is simply too slow to cut it at SS.. when moved to OLB he has decent speed and is better at pass coverage than any other OLB options.. In the middle you want Vilma because he is a monster and M. Mitchell because of his really good speed for a linebacker