Any 1970s Mars mission would have ended in death. There is too much radiation for manned spacecraft of that era (our ours) to handle in deep space.
Would a layer of lead foil throughout the craft make a difference? Weight would be a problem, I suppose.
No, the radiation wouldn't be fatal, or even much of a problem. There are detection systems to warn of heavy bombardments, which are brief, and sufficiently heavy shielded shelter would be included in interplanetary craft.