Barch, ice it and see a physio if it doesn't get better. Start positions seem to be worked out by predicted times for finishing. But then strangely, there always seem to be a big bunch of slower runners, behind the elite runners, at the very front. Hope the Achilles sorts itself out.
Dave928 - or Westoe Rugby Club (just Google them) often allow camping at their ground for the event, it is walking distance from the finish and near Chichester Metro station, which will take you right through to the start line (Haymarket metro and follow the crowds).