The SIC codes are actually updated every decade, however they did not change very much between 1940 and 1960 (a brief history of SIC codes can be found in the “History” portion of this technical document). However, as you mention, it would be much easier to correspond IND1950 with SIC codes from 1972 and then use the resulting crosswalk for all of the decades you are interested in. The second half of the answer you linked to actually provides a pretty good framework for generating such a crosswalk. Since you are interested in the 1972 SIC codes, you would want to download the 1980 census file with both the IND and IND1950 variables. You can then select a single case from each unique IND1950 code. The result will be a crosswalk of single, unique IND1950 values and their corresponding IND codes (there may be multiple IND values associated with a single IND1950 code). You will then need to find the correspondence between these IND codes and the 1972 SIC codes using the codebook from 1980. All together this will yield a crosswalk between the IND1950 codes (which are consistent across decades) and the 1972 SIC codes.
I hope this helps.