The guy has run 70 mpw for years and claims to have a resting heart rate of 23 BPM. He doesn't seem to follow any kind of structured training regimen, but he does do a lot of cross training (including cycling) and keeps a strong core. He's in his early 40s, so he's somewhat off his peak, but he still has the potential for some pretty fast times.
I'll go with 2:52 in a big positive split. He has a lot of talent, but he hasn't done any marathon specific training. If he ups his mileage and follows a proper marathon training schedule, he has the potential to be a competitive masters runner on the local scene.