first question is how long is long? I do brevets (double metrics, 200K or 124 miles), but that's probably too long for you
Two things to remember
1. eat what you can take in, not what you've lost
and
2. HRM 's LIE Well, not really, but often times, the Calorie counter figure is more of wild burro-ed guess
As far as the first one goes, You probably can't put that much stuff down and keep it down. Your body need to burn calories to digest the food your'e putting in and move you down the road - I'd suggest looking at Hammer Nutrition's guides (and keep in mind they're trying to sell you stuff )
As for me, I used to be morbidly obese. If I ate like a normal cyclist, I'd be back at 340 in time.
I usually like to have a big meal before a big event - actually I found that what's on the menu doesn't matter to me. And part of this finding out what works for you - play around and see what you and your body like