Is the editor saying you have to upgrade or is he strongly suggesting you upgrade? If it's the former, make sure the job is going to pay enough to cover the cost of the equipment. Still, the D70 is an older model so you would have to buy it second-hand and so the editor is not being too demanding I suppose.

I'm not familar with those specific lenses to say that those are wise choices. But I do recommend that you concentrate more on the lens purchase than the body choice.

I think September gives you enough time to get comfortable with some new equipment if you act now. If you are going to do this, don't wait until the last minute.