Another item about welding aluminum. You do not want to weld on 6061-T6 aluminum. Espically near those tapped holes. It is an excellent way to loose the heat treat and thus most of the strength of the 6061-T6 aluminum. Tensile strength drops from around 60kpsi down to around 10kpsi.

That makes it easy to strip the threads.

If you are set on welding you might try getting an aluminum in the 5000 series. It dose not rely on heat treat for it's strength.

BTW: About the plugs, I looked at my original handle, the screws only go about half way thru the handle. Plenty of space to install a pressed in plug.