That's what I'm planing to do once Victor Arms starts manufacturing. There are 2 things I'm concerned about. One is that the lower can accept a centerfire upper. Fix: weld a bead on the front take down pin so it's too big to be pushed through the hole(only if necessary).
The second is that the caliber is printed on the side of lower reciever. That's why I'm going to use my Dalphon lower, since it says "multicaliber" instead.
As far as the law is concerned, I'm not sure, but I'll take the above steps to protect myself, especially shooting at the ranges next year when my AR goes into hibernation.