Re: Converting Medium Brood Chambers to Deeps
I think I would put the deep with foundation right on top of the mediums to start out. When the bees move up, start drawing out comb, and the queen is laying in the deep, add a queen excluder under the deep. (make sure the queen is above the excluder)
In a few weeks when all the bees have emerged from the mediums you can reverse all the medium boxes and put them above the deep. Then you'll have plenty of overhead room for either an unlimited broodnest, or supers.
To everything there is a season....