Is an old survey plan ok to use?
Yes it is, providing that the footprint of the building (the location of it's foundation) has not changed. Survey plans that show buildings (called Building Location Surveys or Surveyor's Real Property Reports) typically show the distances between the corners of the building and the property line. This information is invaluable because it allows you to take those measurements and approximate where, on the ground, the property line is. If the foundation of the building has not changed since the 1957 survey plan was done, then you can use it to determine where the property line is.
There is one significant warning in the above advice: you and your contractor are not surveyors, and so any use of the survey plan to determine where the boundary is must be considered just an approximation. You're making a significant investment in a patio, retaining wall and bushes, so you may want to protect that investment and consider bringing a surveyor in to mark the boundary for you. That way you'll be absolutely sure. The last thing you want to do is make a mistake and build in the wrong place!