Hi,
my own thoughts for what it's worth is that you may have a problem with the 3rd gear syncro. If it was the clutch, in my experience of this is you would have clutch 'drag' in gear with the clutch pressed and there would be considerable difficulty in selecting the lower gears while the engines running. You have a more unusual problem. The reason I suggest the syncro is that part of the mechanism is a cone type clutch as well as an interlock device that helps to retain in in gear. If the interlock has started to break up then it is possible that it is jamming the cone clutch of the borc ring onto the 3rd gear and providing partial drive in neutral. The job of the cone clutch is to misalign the teeth on 3rd gear and the hub assembly and prevent selection until their speeds are syncrnised. It's probably no coincidence that you can't get 3rd and there's a 'dragging' in neutral. If I'm right it's a gearbox strip.
The noise when you press the clutch could be either the release bearing or spigot bearing in the end of the crankshaft. If the noise is instantanious then I would say release bearing, if there's delay after the clutch is pressed then the spigot bearing as it takes a little time for the input shaft to slow down and thats when the bearing starts to rotate, could be tricky to deside if there's a drag in the box. Either way the box has got to come out. Check the clutch while you're there and see if the box input shaft is difficult to turn by hand in neutral without the output turning, if there's no problem it will be and that way you'll know which way to go
Hope this helps
Jules