I visited the WTC twice...took the subway both times.IIRC the subway station I stopped at was in the basement of the complex...but I cannot swear to that.
Yes, that would have been the 1 train at Cortlandt St. The only other train in the lower level of WTC was the PATH from New Jersey.
1987 https://www.youtube.com/watch?v=qH0Zc7uJSis
World Trade Center Twin Towers Rare WTC Tour Before 9/11 - 1987 - Part 1