hoorah, it looks like you have some coding skills... It'as been a while since I last spoke with the developer of Navit but I know he would be more then happy to have someone submit a patch for converting units. You can contact him on the #navit channel on freenode.net. He goes by cp15 and monitors the channel quite often. If you don't get a response right away try back in a couple of hours. He is in Europe somewhere so you will have to account for the time difference.

As for the highway name thing, I just submitted that yesterday as ticket 408. I to would like to see a fix for this issue as it can slow navit down quite a bit.