Best plug for tired engine

[Slik69]

I am wondering what's the best plug to run in my tired dog. I am building new motor, but I need this thing running better in the meantime. It's running ok, but seems to be using very very much gas. I mean a lot considering how far I have driven it. It's an old 327. Does anyone know where thes liked to be timed. I have a quadrajet carb and HEI. I just think I have plug issues that could be contributing to this. I don't know if they should be hot or cold plug. I am getting mixed information.

Tired motor, little blow-by, no white smoke from tailpipes, runs good. Idles poor. Have to drop her in drive at stop light sometimes not because it will shut off, but because you know it shoudl be idling better. A friend of mine thinks the motor is good, but I suspect it's tired.