Both Kovacevic and Barron are affordable RD choices. And neither one is old, especially for D--Kovacevic is still only 26. I think either one could be a fit for the Habs' D corps, but probably not both. The decision between the two will depend not only on their skills but also on which style (offensive or defensive) is a better fit--and which of the two will have better trade value.
But, yes, I agree that both can be credible NHL D-men, although probably not both of them in Montreal.