I'm replacing the carpet in my '67. The underneath of the old carpet is soaked with an oily residue. I'm guessing this is from the factory sound deadening material? I don't have time to replace that so I'm wondering if you guys know any good tricks to isolating my new carpet from the old oily stuff.

The oily residue may have been caused by a leaking heater core. I doubt it is from the factory sound deadening material.

That's a good possibility, Mark. The heater core has been bypassed so it's probably bad & was leaking previously. There was residue on the driver's side but it was much thicker on the passenger side.