Every record that requires/required stock heads or when that's all that was available, so a lot
Record machines, especially as time has progressed are BIG DOLLAR cars. I have a set of eddy RPM heads that flow 345cfm. They weren't cheap. I can't imagine what it would cost to attempt to squeeze every ounce of hp out of a set of iron heads, not to menaiton the R & D and the failure yield involved.
