It looks like displaying the history map as a content overlay using KML files might be the way to go. Google earth help has some info about this. There are a bunch of google earth tutorials http://earth.google.com/intl/en/userguide/v4/tutorials/index.html and other resources available from this link.

I also found a page with details about how to import images into google earth: http://earth.google.com/userguide/v4/ug_importdata.html

It has this section on Importing Imagery:

“You can open GIS imagery files in Google Earth Pro or EC and have the files correctly projected over the proper map coordinates in the 3D viewer. Google Earth Pro and EC support the following types of GIS imagery:

• TIFF (.tif), including GeoTiff and compressed TIFF files
• National Imagery Transmission Format (.ntf)
• Erdas Imagine Images (.img)

In addition, you can also import the following images. Because they do not contain projection information, you must manually edit their coordinates for correct positioning:

• Atlantis MFF Raster (.hdr)
• PCIDSK Database File (.pix)
• Portable Pixmap Format (.pnm)
• Device Independent Bitmap (.bmp)”