In short - yes, it can be done. I have a 277 AM (338 LM parent case) built on a Rem 700 long action that came with a standard magnum bolt face. Kirby built the rifle, so I know it can be done.
The problem is the bolt face itself. Most magnum calibers require a bolt face of .531-.534 in diameter (including the RUM's). However, the Allen Magnums are based on "fatter" cases that require even larger bolt faces than standard magnums. For example: the 270 AM is based on the 330 Dakota case (.545 bolt face). The 277 AM is based on the 338 Lapua case (.588 bolt face). In order to build an AM on a std. Rem. magnum bolt, you need to open the bolt face to accommodate the "fatter" cases. This is done by removing material from the bolt face and opening it up. The Dakota isn't too bad, but the 338 Lapua is so fat, that there is little material left around the outside of the bolt face - making it weaker (or at least the weak link). my bolt face has just a thin rim of metal around it.
While it functions fine and is safe to fire, it probably is not ideal for anything based on the Lapua case. I have heard that many gunsmiths simply will not do it because they cannot/will not be able to guarantee the strength of the bolt. Kirby has done them, but as others have mentioned - time may have become so tight that he no longer wants to mess with them.