Do you mean a Mac logic board? A MAC logic board doesn't make much sense; Mac (as in computer) is not an acronym. MAC stands for media access control and is the 48 bit number used to identify distinct nodes on an ethernet network. The chip which holds the MAC address on older ethernet boards can hardly be considered a logic board.
I think you can do it pretty easily with a 74LS14. As far as where to pull the video signal from various Mac motherboards, Google will probably help you with that, or if you post which board you'd like to use, perhaps someone here can say.