If you’re over 29” and have submitted your form 1 you can put a stock on it. The ATF sees the brace as a stock so there is no difference. The only reason to use a brace would be to comply with the MD braced pistol being less than 29”.If you're OAL is above 29" and you otherwise comply with the copycat rule's feature test, you're fine to put an actual stock on it once you get the stamp. If it's under 29" or you have too many evil features you'll need to keep it braced while in MD since those rules don't apply to handguns.