I just bought a laminated Richards Microfit stock for a blind mag, then milled out the bottom for the detachable mag. The only fiddling I had to do was to "move" the front action screw hole forward slightly. I was pillar and glass bedding the whole thing anyways, so it didn't matter. Works and feels great. As for the long action, I'm not sure if you would even have to alter the screw spacing (as far as I know, they haven't changed the spacing for the long action; just the short action). You might have to mill out the bottom of the stock for the bottom metal and then just inlet.
Erik.