Mark,
Your printer conversion work and the write-up is great!!
I worry though why the second printer is not performing as well as the first one.
It also sounds promising that 1.6mm boards can be run through without extensive modification.
Finally, have you tried my printer resolution test:
http://www.vinland.com/USAF-1951.html
See the second part. It gives worst case combinations of slightly angled traces with different track-spaces.
Bertho