For the last two weeks, you might swap one of the zone 5 race-pace days for a day of really hard 1min efforts. Tuning up anaerobic capacity a few times will help you dig deep if there is a steep pitch, or in the last 1-2min of the climb.
(basically, look at how a rower would tune up for a 2k with 6 weeks to go – your effort is about 2min longer, but it’s the same basic game)