Ford 5000 diesel steering box oil fill hole

[Steamboat]

Can't access this fill hole since the plug is located under the seam of gas tank. I looks like a 1/2' square indented plug. No room to get an Allen wrench on it because there is only about one inch space under the fuel tank. I thought about grinding down an allen wrench, but I can't find a 1/2 " SQUARE allen. Anyone encountered this problem?

 

[Harry in Ky]

Make your own wrench using a stub of 1/2" key stock and weld some sort of handle on it.

Or use a stub of key stock and a 1/2" end wrench.