I am aware of the IPUMS ASEC files going back to 1962, and the monthly files (albeit without data dictionaries) going back to 1976 hosted at NBER. Is there any source for the monthly files before '76? When does IPUMS plan on releasing the IPUMS data going back to '76?
Expanding the number of basic monthly samples and variables is one of the major projects for this year. Unfortunately, it is not clear at the moment how quickly IPUMS-CPS will be able to make the 1976-1988 basic monthly samples available. As far as we know, basic monthly CPS microdata do not exist prior to 1976.
Sorry that I could not be of more direct assistance.