what's the compatible gearboxes for this engine 3TGTEU. So far knew one gearbox that
is compatible (w55). Any others? Will K40 gearbox fit in this engine?

Perhaps you should give out more information about the manufacturer, the car, the engine and the gearbox...

T40, T50 W55, 57, 58, i supose any toyota gearbox with a split case.
A k50 wont fit on unless you find a k50 with a bellhouse for the t series!
Also any g series bell housing will work as they are the same as 3t, the clutch slave is on the wrong side though!