actually, I don't see any evidence that that exodus happened at all.
I suspect that you are right, that the leviticus was written around the time of 2 kings (when, these 'old scrolls' were found in the temple.. which amazingly enough gave the current set of priests power as the spokemen from god).
Many of the restrictions appear to be what the religous ceremonies were for competing religions in that area. Amazing.. god give the exact restrictions so that people can participate in other religions ceremonies.