[Proj] Need help converting Goode to latlon

[David Turover]

I have shapefiles made in ArcGIS that use the Interrupted Goode Homolosine
projection. I am trying to use libproj to reproject them to lat/lon, but the
resulting shapes do not align correctly to the corresponding features in
Google Earth. Everything is pulled to the west by a small amount near the
equator and a larger amount further away from the equator.

Example: http://segfault.cs.sonoma.edu/~dturover/gisbug/projectionError.jpg

The projection in ESRI format is Goode%20Homolosine%206378137%20sphere.prj
in that directory. The proj arguments that I am using to define Goode are:

+proj=goode +lon_0=0 +x_0=0 +y_0=0 +a=6378137 +b=6378137 +units=m +no_defs

What sort of things might be going wrong here? How might I be able to
adjust whatever algorithm is being run to attempt to fix it? I am too new
to projections to know what is possible in these areas.

I see that the .prj file has a "<custom>" datum, but I do not know what
this implies or how to make sure proj is using it. The custom datum is:
DATUM[
        "<custom>",
        SPHEROID[
                "WGS_1984_Major_Auxiliary_Sphere",
                6378137.0,0.0
        ]
]

Also, proj -lP lists PCyl and Sph as different projection classes under
+proj=goode but I cannot find anything in the proj4 documentation on
how to specify a projection class. The .prj file says that I should be
using a spherical projection. If proj defaults to a pseudocylindrical
algorithm for Goode, would it produce different results? If so, how
could I force it to run a spherical algorithm?

Thanks in advance for any help.

 - David T.