Quoted from fattrain:

I think I read somewhere previously where someone replaced just one block and ended up with a slightly different contrast in color of the LED's so try and double/triple check with whoever you purchase from that these will be the same exact color e.t.c. otherwise you'll have one funky mis-matched color block in your display....

Quoted from prock:

Out of curiosity does anyone know if these are common anode or cathode? What about the exact dimensions of the housing?

Quoted from prock:

They probably work, but I wouldn't count on the color to be the same. They need to be common anode 8 X 8 1.8mm modules according to Schwaggs previous post. I see a lot of 1.9mm for sale on ebay but very few 1.8mm. What are the actual dimensions of the housing?
These are 1.9mm and there are a whole bunch of these on ebay:
ebay.com link » 60 Pcs Dot Matrix Led Display 1 9 Mm 8x8 Red Common Anode 20x20mm 16pin
These are 1.8mm and are the ONLY ones I could find on ebay (after only a couple searches admittedly):
ebay.com link » 2x 8x8 Led Dot Matrix Module 1 8mm Ca Red Common Anode