mtb101 wrote:get yourself a HRM if you want to do intervals right
I have nothing to contribute on the training front, but I'd definitely recommend getting that HRM, and on the event, set it to beep annoyingly at you if you go over about 75% MHR. Comfort issues aside, you should be able to go pretty much forever at <75%.
That's how I approached my 250km ATBIAD, having never ridden further than 160km and only doing one >100km "training" ride in the 12 months prior to the event. It was definitely useful in the rolling hills between Geelong and Portarlington... when the beeper told me to slow down, I let the group I was riding with disappear over the horizon. But I made the distance.
Bigger hills like you'll find on the way to Newcastle... just make sure you have low enough gears so you can trundle your way up without burning too many cookies. You'll make the distance. Especially if you've done some training, like I didn't.