"If we know where we want to go, then even a stony road is bearable." ~~ Horst Koehler
As others have said ride your bike and give yourself a solid base. The year I rode RaIN I made it a point to ride numerous centuries prior to July. I rode several back to back centuries. I rode and rode and rode some more. Some may say I over prepared but I felt great on the ride. My body handled it well and I felt absolutely wonderful at the end.
I made it a point to drink every five minutes or so. I alternated between water and Gatorade (I like it and it works for me). I also used Shotbloks about every 30 miles or so.
For me, finding a comfortable cadence was the key. Once I settled in and found it it simply became another day on the bike - one I enjoyed tremendously.
Go for it. Find a group to ride with and work together for it will make a difference in your day. Don't think of it as a 158 mile ride but break it down into smaller segments (SAG to SAG). Don't linger too long at the stops - get what you need and get back on the road - too much time off the bike can be hard on the body.
With the cold weather months lingering ahead think about getting a trainer so you can still ride on a daily basis. Time on the trainer will put you ahead of the game once the warm weather returns in the spring.
Hope this helps. Be safe and have fun.
Marcie