It would be possible to make a CP/SP locomotive of the era I am shooting for, but it'll take some work.
I happened across a site with a few photographs I hadn't seen and discovered this shot:
SP 1226 was formerly CP 149 "Diana" from another set of Schenectedy locomotives of the same design as those you mentioned. This image shows the locomotive as an oil burner, with a standard Harriman cab but it does show what the locomotives were starting to look like around the turn of the century. Interestingly the same site shows a few examples of what the motive power I would need looks like including one of ten wheelers I was talking about. I'll have to hunt for an earlier shot of Diana, I know I've seen it before. A lot depends on what A. J. Stevens had done to the locomotives. On the page below note the image CP 168, per a discussion elsewhere it was noted that by the time of the photograph, only the frame and cylinders were original, everything else was built by the CP in Sacramento under Steven's guidance. This is the reason for the extremely thick driver tires, it was done to match the preferred standard driver diameter.
It would be interesting to find out where the locomotive was rebuilt, as that would give a date to when the domes were changed. I'll have to do more digging when I get home.
As for converting the Jupiter model: Why not do it anyway? Obviously there are some safety appliances that could be added, but the locomotive could be easily repainted for a slightly later scheme (1870s) without much detail change.
What we really need is V&T Dayton... Then we could repaint it into a number of CP locomotives.
Though now I want to repaint the Jupiter into something else... We could repaint 119 into the CP versions of the Rogers they owned as well...
Maybe someday, ages from now, I'll endeavor to make a "1876 Donner Pass" route or something. 1876 being picked on purpose so I can include the early NCNG.