DWG-4320 rev A is a 6061 housing, 6 pieces. The pocket floor is called Ra 1.6 and the rest of the part says nothing. The floor is 64 mm wide. I am not sure a 12 mm end mill gets there without a second pass.
Ra 1.6 on the milled floor of DWG-4320
Ra 1.6 on one floor is a finish-pass call, not a whole-part polish. A 12 mm mill can do it if you leave about 0.15 mm and keep the step-over small. Do not put Ra 1.6 on the walls unless you mean it. Is the floor a seal?
We milled a 60 mm 6061 floor with a tired 12 mm tool and the profilometer read Ra 3.1. A fresh tool and 0.12 mm stock left the next one at Ra 1.4.
I will leave Ra 1.6 on the floor only and add 'seal face' so it is obvious. Walls stay as-machined. Please quote the 6 pieces on the 8–10 day tier.