It is not clear to me whether randomc or keyfitz identify the PSUs. What is the difference between these two variables? I can’t locate the stratification variable. Are there any other ASEC data where income is collected as a continuous variable?
RANDOMC and KEYFITZ are included in the original 1968 ASEC file, but the original 1967 ASEC file does not contain these variables. Rather, the 1967 file has a PSU number for each person and family: HPPSUNUM and HFPSUNUM, respectively. I recommend contacting the Census Bureau directly for further guidance on the difference between these variables found in the original CPS files.
Sorry that I could not be of more direct assistance.