At the Youtube site, https://youtu.be/06hk5PzoZPo
Iara Mandyn does a fairly good job showing one real equalizing/clearing technique that was used.
She obviously never DH'd much before she made this video. Check tank position, etc. That said, the equalizing technique was used as well as pushing up on the bottom of the mask, or even forcing the mask hard to the face and blowing through the nose. Some divers used nose clips a la' escape apparatus type inside the mask to equalize without having to go through this rigmarole. A foam neoprene pad is definitely something that divers were using "ad hoc" before companies started installing them. Eventually companies and retailers started marketing nose pocketed masks, which were sold as an upgrade and more expensive "Professional" mask type in the 50s. Nowadays all modern masks have equalization pockets. Incidentally, K Mart was selling these Japanese made (Kunigawa) padded masks as late as 1979 for $9.97.