I went through this myself a few months back. I started drilling progressively larger holes down through the center of it, intending to use an easy-out once the the hole was large enough that the bolt head would fall off. But once the hole was large enough that the head fell off, I found that the load on the threads was reduced to the point that I could use a hammer and chisel to rotate the remains of the bolt counter-clockwise and it unscrewed quite easily.

I'm not familiar with the 740 rear axle and its plugs but if it has
a protruding head, can you not use a pipe (Stillson) wrench? Once you
get it out you can get a new plug and maybe a round or two of teflon
antiseize tape will keep it from getting that bad again.
--
George Downs, Bartlesville, Oklahoma, Central US

I guess this must have an internal hex?

Take a square handled cold chisel that has a blade width slightly wider then the longest dimension though the middle of the hex. File the sides of the cold chisel on a slant so that you get two sharp edges that will bite into the hex when you turn it counterclockwise. File the cold chisel sides just enough so that you can drive it into the hex with a hammer. Grip with a wrench and turn it out.

One thing I did learn along time ago, if you are going to drain anything. Make sure where ever the filler is, you can get that off first.

Very important to use six-point sockets on seized nuts. Can you file off the rounded corners enough to get a six point on it? If you have to file down one socket size, do it.
Other tips:
-Heat it with a torch, then when it has cooled somewhat spray quality penetrating oil on it. Spray over a couple of days to allow penetration.
-Cool it with electronics freeze spray to shrink it, then spray immediately with penetrating oil.

Use antiseize on reinstallation, as this area receives lots of road salt.