I don't think tip to tip is necessary unless one gets a modified version with a longer tube and uses a Loki K motor. The stock sustainer tube I believe is too short for the K. I believe if you rough up the tube and the root edge of the fins, a reasonable fillet of
rocketpoxy or Proline 4500 or if one has any Cotronics leftovers lying around and you'll be fine for flight. If you want to make the can more robust by laminating fine but I don't think it's necessary for a J motor. My GD is going to use a 720 case or shorter
so largest I can use is a J500. I'm not sweating it.
Oh, captbk may or may not have flown electronics that records the info you seek but you can see if he responds. Kurt