After replacing the diodes and resistors on the convergence board I was able to achieve very good convergence, mostly off in the upper lefthand corner. The single remaining issue is the picture is off center to the right. There doesn't seem to be any centering control on this chassis. The yoke seems to be straight and can't be canted on way or the other very much. So, the question is: why would it be off to one side? All my older sets have centering controls so this new fangled design is different than what I'm used to seeing.

Are you sure the picture is off center? Could be your signal source having incorrect H blanking. Try another signal source.
If that checks out, and the set does not have H centering circuitry, the the problem is most likely leakage in the cap that's in series with the H winding of the yoke.
And that would affect your convergence job you just did.

Some sets didn't use electronic centering but rather permanent magnet based centering.... Most Zenith color roundys had a couple loops of fishing line leaving the deflection yoke that adjusted the centering magnets.

I think its a 25" tube set.
Another thing it could be is the low voltage power supply is running low. And that would throw the convergence off too.
I wish I still had my 21" Heathkit roundie that my doctor gave me when he updated to rectangular.

The GR25 probably has a built-in dot generator like many Heathkit TV's do. So its probably not a H-blanking issue.
But it could be a weak 6JE6 issue. The last time I checked those were very expensive.