Eaton fuller drain plug stuck, will my impact work to remove it?

Smack it with a hammer flat on the face once or twice. Shock tends to loosen them up.

 

Or weld a nut to it.

 

Should be two drain plugs on it. On mine, I can't get the lowest one out, but the other one gets 95% of the fluid drained. You really need some actual square drive sockets. (so do I) If shocking it with a hammer doesn't work, take the cradle off your floor jack, and jack up against your breaker bar so it stops trying to cam out of the plug. Might give you the edge you need.

 

Try using the right size wrench or an adjustable with a Long pipe.

Just make sure you are completely on it, do not hurt yourself.