try google or the search button you'd be amazed to see what you might find...
google the term "ps2 versions" ... the very first link will tell you everything
by the way it's a v5/v6...you don't have to worry about gap bios in a v5/v6
you can't go by just the electrical warning (I've got a v7 and a v9 that have it)
best thing you can do to confirm v5/v6 is check the screw inside the expansion slot (check the picture on that page on google)
also what chip are you trying to install? I probably won't be able to help on that front but anyone who can will need to know that...
NTSC V7 PS2
-Matrix Infinity v1.54
-120GB Maxtor DiamondMax HDD