It is easily possible. The running will help with your general fitness level, which is important. Personally I'd like to see your peak training week at about 150 miles, woth a long ride of, say, 75, but what you're proposing is quote feasible.

There's a sticky in the long-distance forum offering tips on riding your first century. One of mine is "start slow, finish fast". If you ride the first fifty miles of your century at a fractionally lower pace than you have ridden your long training rides, you'll be in great shape for the finale.