General Fitness & Nutrition: Cycling training tips for runner...

Hi!

I am more of a runner then a cyclist having run a marathon last weekend But since I like to train and I love project, I have planned to ride a 200km next spring for a charity cause... . So I am looking for information and a training program that would have both cycling and running. I have looked for duathlon training program but I don't find any free on the net... So I have a few questions...

Do you know where I could find a training program?

Do you train the same way for a marathon then for a 200k cycling? This ride will be paced to 25-30km/h, should I speed train?

Is it realistic that I continue training for both a marathon AND 200k cycling (assuming there is more then a month between them)?

Anyone has ever do something like that? Any tips would be appreciated!