Yenko Temp Gauge

[Chuck_Burg]

Does anyone know how Yenko, or other HP dealers, routed the mechanical lead through the firewall? I understand most super cars used Stewart Warner 2-5/8 mechanical gauges. I see the tube runs along the intake/valve cover but where did they enter the firewall? Did they just make a large hole in the firewall behind the motor and use a grommet to protect the tube? I'm wondering because the hole would be larger than a factory oil pressure line hole. Any info or pictures would be great! Thanks!