904/727 dimensions

First, unless you are making a one-off adapter you cannot use a 904 on an EarlyHemi. The starter on the 904 sits about ½" higher than on a 727 and will hit the block. In order to use the 904 you will need to slightly rotate the trans CCW to drop the starter position.

Beyond that, use the trans mount as is/where is and allow the engine to move forward. This will provide some, but not much, additional space behind the cylinder head.

.