I posted this here and on Uzi Talk, and Uzi talk holds onto stuff much better than this site.
Legally, you have to modify the fixed stock's adapter to eliminate the Quick Detach feature. In essence you have to use tools to disassemble it, in order for it to not be quick detachable.
The approach I describe in the link uses your original wood stock adapter and, if you desire, your original stock bushing.
It's not all that hard to do.
1) You shorten your stock bushing (or you can order another one and shorten it so that you can go back to the folding stock if you wish),
2) the adapter has the lug ground off and is then tapped for a pair of new purchased allen screws that are then shortened to the required length,
3) the two stock screw holes in the stock under the receiver are very slightly modified with washers inserted to support the screws, and
4) the stock itself is slightly relieved under the tang to clear the stock to stock bushing screw.
I've never encountered a stock screw and bushing that would not come apart, but with enough rust, or with a needless application of lock tight anything is possible. If that was the case and it would not come off, I'd just drill or grind the head of the screw off and order a new one along with a new stock bushing. The buffer has to be removed as well to remove/replace the bushing and they are a pretty snug press fit.
The method described in the link avoids any drilling, tapping, or modification of your receiver and avoids anything intruding inside the receiver. Once the adapter is modified, you'll have to remove a wood screw and 2 allen head screws to remove the stock, making it ATF legal, but without altering the appearance of the stock. It's also more secure than a QD stock with no rattle or play.
Adpating a military issue fixed stock for use with a non-SBR carbine.
Another option I have toyed with is using a piece of wood or wood filler to fill the recess for the stock release lever in the stock, sand it flush with the stock and then drill a small hole through the filler material to allow a tool like a small allen wrench to be inserted to depress the stock's release lever. It's more or less the CA legal "bullet button" magazine release approach applied to make an Uzi wood stock "fixed". The downsides are the work involved in making and installing the wood insert, refinishing the stock, and losing the look of the original stock release lever.