This can be read with our mac zip drives with no conversion needed. Copy the file onto your MacData folder and retain the zip disk as a backup of the original unaltered image. Make sure the map is aligned square. If the border veers out of view, the image will need to be rotated, which is very likely. Angle corrections will generally be from 0.05 to 0.1.
Guides are useful to make sure the map is aligned and to judge how much further rotation is needed.
To place a guide, zoom to map border, make sure rulers are on, hold the mouse button on the ruler at the top of the image and a horizontal line will be dragged onto the image and placed where ever you let go of the mouse button. The same can be done with the vertical ruler to get a vertical guide. The image must be cropped so the upper left hand corner of the topo is the upper left hand corner of the image. Click on the image and drag open a box on the image. When the box is in place, double click inside the box and Photoshop will cut off the edges of the image.