Rear Diff Plug HELP

[Diastole]

I am new to Model As. I have a early '30 coupe.

I want to change the diff fluid. This car sat in a garage since 2015.
Owner recently passed, sadly. Rest his soul.

The fill-drain-plug has half of the lugs sheared off. I am looking for some help for a possible solution on how to remove it w/o damaging the housing.

See photos

I can try some vice-grips after heating the metal housing. Or, drill a hole, tap with left hand threads, and install a left hand thread bolt. Or weld a 3/8" square bar in what remains of the plug.

Being Model A's are new to me, and my interest to not reinvent the wheel, I am asking for any help or suggestions I can get.

I can do two of the three thoughts above, I do not have left hand tap and die set.

Thanks in advance

Diastole in the Smoky Mountains