I've made a test build which may resolve zebra and OSD issues on this camera. This assumes it is a the same display layout as sd990 and d10. I think this is likely but I don't have the camera.
edit: mistake in previous build, test2
builds removed, see later posts
Should do the following:
OSD should be larger
Zebra should work (memory permitting)
Histogram should have proper aspect
standard CHDK grids should work (colors may vary)
Games should have correct aspect too, but they are disabled in this build to save memory for zebra.
Note, you should probably remove/rename your existing CCHDK.CFG, or OSD items may have remembered positions from the old screen layout.
edit:
I should probably link the right build
edit #2
mistake in first test build, I've uploaded a new one. This also has some changes that might fix diskboot start.