I just drained my 1985 Z-28 305 4bbl radiator yesterday. It is located on
the lower passenger side. It is not a metal petcock but a plastic thumb type
screw. Get it loose then pull on it until the water starts to drain. It just
has a flat tab that you turn with your fingers. Although I had to use some
pliers to get mine loose. I think you found it anyway.
BTW, since you have the same year and engine, what is your timing settings
supposed to be. TDC or how many degree's advance? My sticker is missing.
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