Is it possible for 318 to run with dist. 180 deg. off ???

No.
The timing mark will be tdc on either #1 or #6 firing, which are 180* opposite on the distributor cap.
You can time a V-8 engine off #1, & #6 cylinders.
A 6 cyl engine off #1 and #6 also,
And 4 cyls off #1 and #4 cyl iirc
His is handy when trying to time an engine when there is an air cleaner stove duct in the way.
There may be a foreign exception.