In response to the United States announcement of manned moon landing plans, the Soviet Union announced the TMK program. This program would have sent manned missions to Venus and Mars. The original mission was just a flyby of the two planets. Several possible variations were considered, some of which added manned landing components on the surface of Mars.
For the purposes of this we can just assume the N1 rocket was a total success. There is no reason why it couldn't have been completed, it is only a failure in history because of poor management and that changes in the political attitudes of the USSR made it un-needed.
Given the technology and knowledge of the era was there any chance the crew even surviving?
By the announcement of this program, multiple manned missions had been made to low earth orbit. But it was not until the manned moon landings of the Apollo program that we learned how harsh even the environment on the moon could be. There are more details about this experiment here. Did the Soviets possess the correct knowledge to adequately shield the crew from radiation encountered during the mission?
Some of the missions had durations measured in years. Even if you could put the crew on a calorie-restricted diet and somehow carry enough food, you would have to reuse water and oxygen while in transit. Did the Soviets posses an adequate knowledge of life support systems that can support such a long duration mission?