You purchased it....well done! It is in EXCELLENT condition
Depending on where, when and by whom it has been deactivated, the modifications can differ.
Making the trigger group unfunctional and welding the bolt is common and should not be any problem for the E11 conversion.
The small weld on the lower edge of the mag well can easily be adressed with a dremel.
Cut the mag loose, clean the mag well/ reblue the bare metal and start working on the magazin. In case you damaged the mag or can´t get rid of the weld on it, get a new one...these are plenty and cheap.
Again...congratulations and have fun converting it