Not sure how well this has been covered, but chassis regidity is all important in how much you want your engine block to twist under loads like launch if you mount the engine solid to the chassis. I get away with it because I have a VERY stiff, triangulated chassis. At the very least there will be some twist in the engine block. It may be immeasurably small, with very little effect on ring seal etc, or like one situation I was told about. It broke a block! Which makes me realize my going from a megablock to an aluminum block may need a forgiving type of mount between trans and block.