I looked at those posts, and it looks like the the importer did something wonky with the link addresses ... they're pointing at random no-longer-existing locations. I'm afraid they all need to be updated. Sorry.
I think we already have the functionality for linking to specific posts? Take a look at the toolbar at the bottom of the post, and click on the link icon ... it's for "share a link to this post." That brings up a popup with the direct link.
We do have the ability to link to specific posts. I'm sorry I didn't look harder before I posted. Please accept my apologies. But now I'd like to edit that earlier work so the links work. I see that I can edit my new posts, but I don't have that option for the older posts, at least not in the same place. Are posts from the old software going to be un-editable for us?