I'm pretty amazed there are so many OEM parts available for a bike from 1970. Makes things pretty easy.
T4
Many people (including some at Honda, sadly...) do not remember Sochiro's famous commitment to his customers, stated in the 1960s: "There must always be made available from Honda the critical parts for our motorcycles."
While he was alive, this was fully honored. The 750 in particular built Honda, so it at least merits some special attention from them, somewhat, today. Fortunately, Honda's habit of designing new bikes from parts they already had has also helped.