CC, I'm sure you can do it, but I'd suggest some training rides longer than 120km. My reason is from my experience. I did a 115km ride last year and the longest ride I did in training was probably about 80km two weeks before, the rest were 60-70kms. I found it made the day a bit harder (so did the flamin hills!) and recovery slower to not have done the distance or closer to it.

I notice a lot of friend who do IM triathlon will ride 180kms around 3 times before an Im (this is average only) and try to do about 3 rides of 120 or 150 as well. Helps get the body used to the distance.

Audax events are great, do check out what they supply as the less junk you have to carry the better. I know there was some stuff provided on the Apline Classic last year, including water.

On the 115km I did, we could order lunch, (a salad roll, bar, apple juice) but carried bars and protein bars and two bottles - one of endura the other water. I have one of those profile rear seat mount bottle holders, so had the tool kit in one and my rain jacket folded up and tucked into the other one. Wore arm warmers and a vest and tights as it was a pretty cool day. It took us about 5 hours - it was those hills and lack of training!!