Mine (25EC58, basically same chassis as 25DC56 except for high voltage tripler and audio circuit), has had slightly too much width on the right side (nonlinear), since I got it at the Salvation Army in 1981. I live with it, but as you found, there is no adjustment for width or linearity. It didn't bother me enough to fool with it, but maybe someone else here has. That's about the best TV chassis ever built, and my opinion on that is shared widely here, and seldom if ever challeneged
You have a great set there.
And RadioTVnut is 100% correct: If yours still has the white ceramic safety caps, REPLACE immediately. May not affect the width issue, but if those begin to fail, the HV can soar, and actually arc over to the yoke and snap the neck off the CRT! Seen it happen many times.
Charles