Sorry about this, but I'm an engineer and cannot let things go if I don't understand them, so I looked this up!
The cessna incidence adjustment facility mentoined above is effected by the bush around the rear wing attachment bolt which screw (to put it simply) into the end of the rear spar. The plain (unthreaded) part of the bolt is a close fit in the bush, and the hole in the bush is bored off-centre. The result is that the bush can be rotated (with the wing bolt loose) to move the rear attachment up or down over a total range of about 1/4inch, and then locked in place by tightening the bolt. The bolt and bush look like this:
Cessna wing rear attachment bolt with eccentric bush incidence adjuster
As you can see, the bush itself is not threaded (internally or externally), so rotating the bush to adjust incidence will NOT push or pull the rear spar laterally, so there should be no sweep changes when the incidence is adjusted.
I think someone was pull your plonker...
PDR