That should already have the mountings in place so it's just a case of finding suitable belts. Have a look around the forum, I've seen a post recently where someone had fitted rear belts to a HC.
I believe so - I saw some photos of a HPF that had rear belts fitted, and I think the lower mount (that is often in the rear wheelarches) was a little further forward, on the edge of where the inner sill meets the floor. Other than that, the C pillar and tunnel mounts are also there I believe. It's a while since mine was in pieces so I can't recall. I don't carry passengers so I've never thought about it.