Sorry to bump this thread but I finally dug up the Sabrina CD and the version of Magnet & Steel by Matthew Sweet (with backing vocals and lead and rhythm guitar by Lindsey, say the liner notes) is
definitely a studio version, like I said. It says it was recorded and mixed at Ocean Way, Los Angeles and Susanna Hoffs also sings backing vocals.
I can post it for anyone who doesn't have it wants to hear it.