Interesting - as Jonny-B says it may be lightweight mobile cranes for the internal remodelling. The steelwork will be assembled behind the existing stand and lifted into place from behind.
If the pitch isn't being relaid then the last thing you'd want to do is have cranes fucking it up.
If that Echo article is right, it appears the club might have a tricky decision to make. Leave the pitch as it is in order to progress the construction of the new stand as scheduled, which could mean we have a bog of a pitch next season. Or sort the pitch out in the summer and delay the work on the stand.
Its difficult to see them going with the latter option because if the cranes being on the pitch at some point is essential, they don't have any other opportunity apart from June and July.