>>1831580That is a seriously fucked up scan. I think it could be further improved, but anything I tried after this point didn't seem to help. I can't explain everything I did, but in summary:
-Fourier transform on a duplicate layer using this plugin:
http://www.3d4x.ch/Swift's-Reality/FFT-Photoshop-plugin-by-Alex-Chirokov/16,35-Set original layer above and set to color.
-Topaz labs denoise and detail
-about 1 px gaussian blur
-high pass filter on duplicate layer set to overlay
-adjust curves
By far, the best thing would be to find a better scan.