Personally I'd leave the powerharrow to one side and get a fella with a horsh drill or some similar and direct drill oncenyou are happy it's level. Don't be in a panic for grass as it will take longer to establish. Mow off the field and let it green up and spray off. Or if the cover isn't to heavy you could spray off and bale up after. But you run the risk of not getting all the old grass if it's very thick. I'd lime then and direct drill and roll the arse out of it then.