Be aware that the 26 CFR 301 regulations are all "interpretive" regulations which do not have the force and effect of law. The IRS acts as if they are law, but they only apply to treasury department employees.
As stated the Parallel Table is not definitive. The more definite way to find out whether a regulation is actually based on a code section or directly on a statute is to look in the Electronic Code of Federal regulations. It has tables which show the authority for each regulation. If the authority is a Treasury document or 26 USC 7805 only, the regulation is NOT a substantive one, There must be a citation of an individual code section (or in some cases a Statute at Large reference) for the regulation to be substantive. This is based on the Administrative Procedure Act and on 1 CFR 1.