Training Plan Help

Hey,

Looking for a bit of help on coming up with a training plan. I signed up for a Gran Fondo in six months time. 165km total distance, and about 2km total ascent, within the first 30km of the race is nearly 1km of the ascent (up a mountain). I have done this distance in the past, but those rides were around 1km of ascent.

As things sit I am 6'1, 157 pounds, and my current FTP is around 225.

In the past I have never done any specific training, other than saddle time and doing what I wanted. I know I need to spend a bunch of time in Z2, but it is trying to figure out some interval training that I am a little bit lost. Not sure if I should be doing more shorter or longer intervals, at what power level etc.

With two small children and work requirements realistically I can commit to about 8 to 10 hours a week. Any help would be much appreciated