Has there ever been an aircraft with a gun permanently aligned
off-center? I don't mean swivel mounted, but permanently fixed at a
point other than straight ahead.

Yes. The Japanese Army Air Force regularly mounted oblique cannon
(aimed upward and forward at perhaps a 30-degree angle) in their
interceptors in an attempt (not terribly successful) to shoot down the
B-29s which they couldn't otherwise reach.

all the best -- Dan Ford
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