The issue with the corners was at Odsal, Bradford after the Halifax Dukes speedway team moved there for the 1986 season. I don't remember the corners of the pitch needing to be moved at the Shay as there was room for the pitch in the middle of the speedway track. In fact just checking some old videos on YouTube shows the corners of the pitch intact as racing goes on. On a Saturday the speedway would start at 7.30 barely two hours after the football ended. The speedway team left Halifax due to financial disagreements with the football club, and were in fact getting bigger crowds than the football team. It wasn't because of issues with the pitch. As the speedway track had recently been relaid at Bradford for the 1985 world championship final a move to Odsal seemed to make sense, although the crowds were never very good when I used to go.