Both the basic monthly and ASEC (March) files from CEPR CPS and IPUMS CPS have the same sample size and can be merged on a 1:1 basis. I found it useful to merge on the following IPUMS variables: MONTH, STATEFIP, HRHHID, HRHHID2, SEX, AGE, and PERNUM. For a more detailed discussion on merging CEPR CPS with IPUMS CPS, see this forum post.
I hope this helps.