Rescanned the front of the backglass just then and much happier with the results. Saved as .BMP files and they total 650 MB combined.

Glad you see the improvement.
Now is probably a good time to save a test scan in different formats, and see how quality compares versus size.
You might find that simply saving your scans as .Gif will have the same colour quality and far less file size, which will allow your photo-editor to breath a little.
.BMP may still default to 16 or 24bit palette size (huge file) while .Gif will typically default to 256 (maximum) Colour-Palette at a greatly reduced file size.......something to play with and find a good working formula for yourself.

Anything except .Jpg is a good place to start hehehehe.

MM.