Get a 1/2" bolt and grind the end to fit the internal square of the bung. Remember to not use a gas torch to unfreeze the plug!!!!!

There is an adjustable tool that expands to fit the exact square hole. I have one and only used it once in 40 years. Send me your address and I'll mail it to you. Of course, you could grind a 1/2', drive down to the correct dimension. The plug is probably stuck pretty darned well after all these years.

I have a drawer full of tool steel pieces for my lathe and found a perfect fit there. I think it was about 5/16" or so ,just put adjustable wrench on it and turn.
May want to cover with rag in case tool steel breaks. But I have never broke one,
Roger B)

You could also grind the end of a 3/8" drive extension down to fit.

I wound up grinding down my cheapest extension and with it I was able to quickly and efficiently snap off not only the plug but the bung it was threaded into.

This thread reminds me of something I will do shortly. My tank has two drains: one at back center and front left corner. They have protruding squares, not recessed plugs. I will replace the front one(lowest) with a drain cock that a hose can be slipped on--$3.95. Allows easy tank draining for cleaning water out or providing gasoline in an emergency. Note this is behind and above axle so as not to be hit. Thanks for turning my light bulb on !!!!

Snap-On Tools has the correct plug remover. It is a hardened tool, and carries a lifetime guarantee. I think the Part # is PPM-411. This is 11/32nds. I have a complete set of these, use them all the time on our Hudsons and have found them to be priceless!

Steve, Glad you found some doors. Where are they coming from?

There was some problems with the doors. I am going to build my door like I had planned.
S