Good luck- I'll be watching closely, to bring my 3:02 down to the sub-3 as well. That's the plan, anyhow!
I'm not sure about Steve's thoughts on your half marathon current pb. Past comments, including those on the RW Schedules, suggest a sub 1:23 (and sub 38 10k) as the right sort of level for a sub-3 marathon. If we need to be able to bang out a 1:21 half then I'm sunk...