Moonischasingme:

I was in a similar situation last year. I went from my longest ride being 14kms to riding the 100km leg of the Around the Bay in a Day ride in October. Did it in just under 4 hours on a flat bar, too, and felt I could have kept riding for another hour or so.

I followed the program here: http://www.bv.com.au/file/file/ATB%2...%20Program.pdf

A friend of mine tweaked the program so the Tues and Thurs ride included intervals, and the Wednesday ride included hills.

Hope this helps and good luck! Let us know how the training is going.