Given the extent to which Unicode is used today, and its broad support in OSes and applications, you should instead be encoding these line-drawing characters according to Unicode. Character 91 corresponds to U+2510, Character 192 to U+2514, and Character 196 to U+2500 (although you described it as a vertical line, it displays as a horizontal line). Unicode is definitely the better way to go about this, and does not have the ambiguity that is present in most legacy encodings.
I tried adding /Encoding UnicodeEncoding and that did not do the trick. It also killed the Courier font which we need becuase of the proportional spacing.
Instead of an actual charater 196 in the data stream, I tried adding U+2500 but that did not work either.
How do you encode these as unicode characters in the data stream?
Although I would love to be able to provide to you the guidance that you need, the details are beyond my area of expertise. You are likely to get the guidance that you need by posing these questions in the appropriate Adobe Forum, specifically the Acrobat SDK one.