Does the brightness PWM frequency has an issue for EMI. I used 500Hz for my sign but didn't experiment with lower frequencies. I thought if I used 100Hz or lower PWM frequency one will notice the flicker if he is driving!
What PWM frequency will you choose?
Since my "color scheme" involves display times as low as 0.5 millisecond I have to PWM at 16 times that frequency i.e. ~30kHz (I can look it up). The 'easy' way to reduce EMI is to use the modern 'improved' SR2221A equivalents (e.g. Allegro) that delay the unblank of the 8/16 outputs by a few nanoseconds from pin to pin.
The lowest useable frequency for unblank, as I found by having everybody (and a few brothers :)) look at it, is 120Hz.

EMI can be greatly reduced by 'local decoupling'

Erik