Swap 904 to 727?

Is it that much work to flatten that joint on the tunnel so the 727 will fit. I will keep that option in mind. Will have to shorten the D shaft some day to receive the 8 1/4 rear end. Every thing I have read says the /6 904 is not strong enough for the 318. Was told by the seller of the 318 that it had a modified cam in it. Don't know if its mild, medium or full. If the 72 727 came from car with 318 in it, why does it have balance weights on it?