Looking at Googe Earth, there are actually two tracks with the Alexander Stadium. While the main stadium is probably not on for speedway, there is no reason (except financial?) why a speedway track could not be built inside the second (training?) athletics track.
Howarth is hardly the first rider to get a flat tyre. No-one else had any problems, nor did Howarth himself later. Phillips was probably trying the same trick which worked so well for Redcar a couple of years ago: make a fuss about the track to put off the opposition.
And this was the only time in speedway history that the referee has had a standing ovation
Joe was replaced at Birmingham because he was injured. Pearson was on a 4 point assessed average, and wasn't scoring anywhere near that; he was replaced by a 2 point rider (who is scoring above that) to free up points for a third heat leader.
No: GMs depend on splash lubrication (the big end running in the sump). Top professionals change the oil every couple of races, and you dump the oil anyway after each meeting.