I saw the FAL buulpup kit at this years SHOT show. I think ACE manufacturing make it (know for making assualt weapons stocks), the owner said he was working on an AR bullpup (I don't know how he is going to move the recoil buffer/spring). There are kits for the Ruger Mini-14/30, 10/22 and other Ruger autoloaders as well. Personally I think the Bushmaster looks pretty hanious and the rail is to high, no iron sights. There are a couple of customized ones on
www.AR-15.com that deals with these issues (I guess there is a gunsmith who specializes in customizing them).