I'd encourage you to do as much saddle time as possible.
A century a month?
There were a couple of other people on BikeForums that are interested in that ride.
https://www.bikeforums.net/long-dist...ifference.html
@
wipekitty, @
srode1, @
rhm
Perhaps you can find a training/riding buddy.
I've hit 200 miles a few times. Not much more. One of the issues I foresee is that there is apparently a 16.5 hour time limit. Unless it is organized to get a strong tail wind, that would definitely be a challenge for me (which is also a reason to do it with a group)