Hi Rod,
Subbing the Trail Challenge riding for weeks 1-2 of the bikepacking plan and taking a deep rest in week 3 is a solid option. I recommend doing lower hours and lower intensity days 1-5 of week 3 then getting back on the plan as-is day 6 and 7.
I do recommend spreading the challenge riding over two weeks, rather than cramming it into 6 consecutive days. This will give you a fitness bounce, rather than pushing you into an over-trained state.
To prepare, stick to the Masters CC Build Peak with a focus on quality and recovery. Take it easy the week of 6/7 so you start the Challenge rested and you will be ready.
Coach Lynda