Davjack is fine - IMO it fits more into the psychedelic vein than a real prog one - outside of "Rondo" and the jam on "War and Peace" it's mostly short, goofy songs. Ars Longa Vita Brevis is the one that I feel really shaped prog rock from '69 on. It's not great but it's pretty good and I do believe its a way more influential album than its given credit for. They tanked hard after that, though :)