arduino and 624 LEDs

[jwflammer]

hello i want to eater use 624 LED's or 39 8X8 LED matrices which is easier and how do i make them operate on my arduino mega? bread boarded first then soldered to a custom PCB.

[Grumpy_Mike]

which is easier

using the LED matrix especially if you let external hardware handle the multiplexing.
Team each matrix with a Max7219 or MAX7221. Then talk to the 39 chips cascaded in shift out fashion like shown in Figure 3 of the data sheet. This method could also be used with individual LEDs as well if you want.

bread boarded first

You would be mad to bread board any more than two of these, you will never do all 39.
This is an expensive project.