Chris,
Sorry to belabor the point, but I think there is way around the problem you mention. If you mount the part off-center from the lathe spindle axis, you would avoid grinding at the center of rotation of the part. That should eliminate the high spot you describe. You would also increase the radius of the grinding marks which would come closer to matching the finish from a surface grinder.
For what it's worth, one way to get your "cheap" surface grinder is to pick up a metal shaper and mount your toolpost grinder on the end of the ram.
For that matter, why not mount your toolpost grinder onto the ram of the milling head of your lathe/mill? You could make a bracket that clamps onto the outside of the ram.
Best regards,
Andy Hall