You're definitely physically ready to run 2:35. I can't speak to your mental toughness, though, and between 18 and 26, much is about mental ability.
I would say try and run even... 1:17:30-1:18:00. Agree that 1:20 is too slow.
I ran 2:39 in much worse shape then you, and if anything, am more a mid-d guy then a distance guy. Only reason I gutted out the 2:39 (2:39:58, to be exact) is because I willed myself to i
The spring before my fall 2:39, I think I was in 2:35 shape, but got sick for a week 10 days before Boston (i.e. stopped throwing up 3 days before Boston). Leading up to that race, I was in the best shape of my life, and still only ran 1:14:55 (though it was a terrible race). I had similar mileage to you but a 4:00 slower 1/2 PR.
So, based on my own training, actual race performances, hypothetical race performances, and your training... seems to me that 2:35 is definitely, 100% doable.