Finally, if you build it into a rimfire rifle then you are allowed one "evil" feature. Just like the old AWB. So you could build an AR in .22 LR with a standard pistol grip, plain muzzle and no bayonet lug.
If doing this, I'd not play it cute by simply putting a .22 conversion kit into an otherwise stock AR since you could convert it into an AW simply by removing the .22 conversion kit.
There are a number of ways to make it more difficult to convert to an AW.
1) Solid plastic buffer tube so a buffer and spring can't be installed and a centerfire bolt carrier group can't be used.
2) dedicated .22 barrel without a gas port.
3) standard barrel with an adjustable gas block turned "off" or a CMMG solid unported
gas block, and no gas tube
If it were me, I'd do a plastic buffer and no gas tube. That way I wasn't spending any significant money on non-223 items, but have still made it so significant work needs to be done for it to be an AW.
Look at it this way. If you do it like I have suggested, but then remove the solid plastic buffer tube and replace it with all .223 parts, you are still legal. The gun would then be a straight pull bolt gun, since no gas tube means no semi-auto function.
Don