Thank you for your comments and information.
The reference map is the esri World Image which esri makes available to anyone. World Image's spatial reference is WGS 1984 Web Mercator Auxiliary Sphere and I used that as the coordinate source for the images that were referenced to it.
The purpose of the mosaic is to provide visitors, including researchers, to the CNMI Archives with a view of Saipan in 1945. I don't know what kind of accuracy and precision they will need. The archives curator says people ask for that sort of thing from time to time.
I would at least like what you might call a nice qualitative map. The more accurate and precise, however, the better for researchers who might want to make measurements or take data from the map.
For reference points, there are a fair amount of coastal features that seem to have remained stable since the aerial survey 70 years ago. In addition, there are some Japanese concrete buildings and fortifications which are still here. I've also used road intersections which in some cases are dead on but in others have moved.far enough that I've had to throw them out as references.
To get an estimate of the photo scale, I measured across a large feature, Laulau Bay, on the scanned map and compared it a Google Earth measurement. The scale looks to be about 1:30,000.
BTW, I recently got a hold of a government sponsored Lidar survey of Saipan and am considering including contour lines on the final product if that's possible. I am also wondering if I could make the Lidar my reference map.
Thanks again.
john