1970 L78 has the low profile intake..so no extra hole...driver's side head is the correct spot...but I don't think you can have both
..pass side head is for the TCS...if you aren't running the TCS system, then this would be the best spot for the temp gauge....never did a T fitting with the oil gauge...I assume it is mechanical..??? I wouldn't worry, the only "idiot" who can see the lights is the driver
wilma