Please verify this, but I vaguely remember reading that the single-stack rifles used a different bolt, one that won't work with double-stack magazines. Replacing the bolt with military surplus is an option (about $50), but you have to make sure that the head space will be correct, and both the carrier and the locking piece have a large influence on that and may also need to be replaced. Also, there may be some dimensional differences in the single-stack receiver preventing the use of a replacement bolt or a conversion. It would be a good idea to verify all that before someone starts cutting into it.