Yes, in '76 there were still 70mm/26tpi bb's being sold. Velo Orange makes threadless BB's. A simple Google search will tell you if there is another or cheaper option. Some study of Sheldon Brown's BB pages, research about the chainline requirements for the cranksets you are considering, and some simple math will tell you what you can use. There are too many variables for you to expect someone else to do the work.