good idea, first breed your lapras to with a power anklet, then with your new full speed munchlax, breed it with your lapras@destiny knot & lovingly lend the new munchlax a power anklet and breed them together.
in theory, the destiny knot should pass down random iv's as the power anklet should pass down the perfect speed of the munchlax, simple.
ps. how the heck do you know the ivs of your pokemon?! don't tell me you lv them up to 100 straight up.
of so, your commited.