Echinopsis for sure, once you loose track of the ID of a hybrids re-identifying it is not that easy - too many very similar looking ones out there. For this one, my guess would be Echinopsis x 'Los Angeles' which is a very old hybrid. It was part of the 'Paramount' collection of hybrids. The body of the cactus looks like a good match for mine that came labeled and the flower does too.