20 week 5k to half ironman (no swim)

I'm registered for the New River Challenge on 17-Sept, which is a 40-mile bike ride, 12-mile kayak paddle, and 13 mile run (all flat). I'm 47, and have been sitting at a desk way too much over the past 20 years, and just a little overweight. I'm in week 6 of the aggressive (16 week) couch to 5k plan (up to 12 min run so far, no prob). Any suggestions for a 20-week 5k-to-13 mile run + 40-mile bike plan? I was thinking of modifying the 20-week Olympic plan by accelerating the running and biking schedule and dropping the swimming.