Are they stripped lowers marked multi caliber or were they sold to you with a stock attached. If the stock is attached and sold to you that way as a rifle lower, then you can’t make it a pistol. You need to sbr it. I may be wrong on this but i dont think so. Stripped lowers can be made into a rifle or a pistol with no registration required for either unless you sbr it. It’s been a while since i looked over the rules regarding pistols. Might want to do some research just to be on the safe side. As long as theyre marked multi then you’re good.