Mal's 1971 album "The Call" is one of my favorites. He plays electric piano and there's also an organ on the date played by Jimmy Jackson (with a very distinct sound, I'd say more rock than jazz, but not a Deep Purple kind of rock). Eberhard Weber is on bass and Fred Braceful on drums. This is on JAPO records, but practically an ECM recording.
I also recommend Mal Waldron's German recordings with Dusko Goykovich from 1967, some of which are available on the (great) European compilations "Forum West: Modern Jazz from West Germany 1962-1968) and "Focus Jazz: More Modern Jazz from the Wewerka Archives 1966-1969".