The 400's from what I can tell were all setup with the 385 series bellhousing pattern from '73 on. In '72, there were some 400 blocks that had a dual bellhousing boss cast in that could be drilled for either 335 or 385 series bellhousings. I had one in a Torino drilled and mounted to a small block C6 from the factory. I still have the trans as a spare for my 351C. I understand 400 blocks with the small block pattern are fairly rare. You will also find it referenced in the HP book on building small block Ford V8's.
Another thing I seem to remember was a 377 cid version of the 385 series that was only used in medium duty 500/600/700 trucks.
Lugnut