R,
Thanks for posting on the forums! My answer was easy…until you threw in the marathon 5 weeks before the 70.3. You can do both, but be prepared that like Solomon splitting the baby, you’ll end up with poor performance at both events instead of stellar performance at one.
Ok, the 70.3 won’t be totally disrupted, but the Marathon will be as you suspect: just a slog fest easy run to get to 26.2 miles.
So, the best (least-bad) option is to re-load the 70.3 plan with your new event end date, just pick up where the plan is for that new end date (about Week 5). This does extend your total 70.3 training to 27 weeks, but that’s not so bad. We like to cap formal training 24 weeks, but a bit longer is OK.
For the week of your Marathon, I need the exact dates of your 70.3 and marathon to make the correct recommendation on how to adjust the plan.
David