go to Big D cycles and look at their on line parts books.
If the numbers don't change as you go forward and backward from 59, you get an answer.
3TA bits may well fit as well.
Once you have a part number, just googling it may come up with an answer.
ie pt no < 1234 Triumph> may come out as "1234 1955-65 model y Triumph thingie"