Make sure to wave at all the people riding back to Cherry Hill on the 24th.

Seriously...In order to assess my fitness, I would plan a long ride with options to shorten things if you feel you cannot make it. You are not a newb. You might be surprised at what you can do even after time off the bike and/or low mileage. This year I didn't do two hard rides back to back, and no ride of more than 70 miles, before I flew out to Montana for a two week, self contained tour of close to 800 miles with more than 41,000' of climbing. The first day of the tour I logged about 90 miles. And it wasn't the first time I had done something like that.