Ok, just had a peek at your drawing and first thing that popped out at me is how close to end the AC bearings are.
Good for rigidity as you said.
In my opinion, and also the reason why SKF and NSK mount their spindle bearings away from the mounting flange, is to eliminate the possibility of warping the bearing seat/head bore during final assembly into the mill head.
But, provided you have clean and flat mating surfaces between the flange and head, you should be OK.
Their are ways around that but that would be giving away my company's intellectual property...LOL.
Either way, looks fine.