1.) I don't think you can do much for the M113. I've gotten in tanks before and sometimes it shake from side to side a little. As long as it doesn't cause problems, I think it's okay.
2.) I also noticed this. I found the right face one time for a mission I was doin. So I made the identity for the .ext and I thought it would work. No dice, I got the James CO from the demo mission...
Try a setface and an identity .ext thing. That worked well for me, well sorta, I better check it now that I think about it.