I think most Wellcrafts have them on the sides just below the gunnals? That should be sufficient. Putting vents on your engine cover will just increase the noise level of your boat.
Capt., I hear ya loud and clear...but I got a feelin' if those boxes needed to be vented, Wellcraft or somebody on this board woulda done it by now...I bet the water flowin' thru the block is ample coolin' ...not that I don't applaud innovation and tryin' new stuff, but I think you're gonna spend some time and money and not accomplish much...