There are several major differences between the full and semi auto modles. The bolt for one thing.
Never did own an Uzi myself though
The bolt has a fixed ‘nipple’ type firing pin. But the biggest problem going full auto is the disconnector. I think it sits in the bolt. The bolt is the majority of the Uzi weapon’s mechanics, it is an odd firearm that way. I may be wrong about where the disconnector sits — I never made the attempt to convert nor even really bothered learning much about it.
l