Re: 159th Infantry Regiment
I can see your point about five rifle regiments to a division, David, but nothing in my references confirms that the 422nd and 423rd ever returned to service with the 106th. Are you sure you "read that somewhere"? I can only reiterate that Stanton says in his narrative of the 159th Infantry, "arrived in France 18 Mar 45 where attached to the 106th Infantry Division throughout European service...".
As for a copies of Stanton, they are a little pricey, but you can find them floating around. Try alibris.com or bibliofind.com