Forgot I took some shots of the process when I stamped the shallower inlet side.
I cut the 3/4" MDF out on the CNC. I gave one side 1/8" clearance for the metal and the other side the circle press fit into the MDF.
This made the die the right depth (I needed it to be stamped 1/2" deep for the right offset). It also made it easy to register the die halves.
Once out of the press all I had to do was hammer the tucks and it's ready to trim to the firewall. The firewall that doesn't exist yet.