Joined: Nov 2006
Posts: 19,810
Likes: 597
From: NJ, NYC, LI
Bikes: 1940s Fothergill, 1959 Allegro Special, 1963? Claud Butler Olympic Sprint, Lambert 'Clubman', 1974 Fuji "the Ace", 1976 Holdsworth 650b conversion rando bike, 1983 Trek 720 tourer, 1984 Counterpoint Opus II, 1993 Basso Gap, 2010 Downtube 8h, and...
I'm thinking you can do it at your current level of training. At least, if someone asked me to do an 80 mile ride tomorrow, I wouldn't hesitate, even though I haven't done that many miles in a day since... oh, I guess it was September. (I'm 47).
Your neck will probably be pretty sore by the time you finish; bring some of your preferred analgesic.
Be sure to eat well the day before, eat a big breakfast, and try to eat more or less constantly on your ride.
If you can go for a 50 mile this weekend, and the same or longer next weekend, you'll have 100% confidence. If you can't do those rides, don't sweat it, I'm sure you can do the 80 as is.