New to old pool

My in ground gunite pool was here when we moved in 35 years ago. I believe it was installed in 1963! We've done nothing to it except try to keep the chemicals balanced every year. Last year it seemed to have a leak at the tile line so we finally gave in and contracted to have it replastered including new tile. We are using DiamondBrite since it supposedly lasts longer than plain plaster but we shall see. I've been reading everything i can find on the start-up process but still a bit worried.... For example, my contractor plans to give it an acid wash before filling. I've read that is less than optimal. Hopefully, he will be able to explain his choice well enough that we can move ahead. I wish i knew who installed the pol originally! 50 + years with almost no problems must be a record...