Well he doesn't say what size brush cutter.  I have a 6 ft, and I just took the blades off mine a little while back. (Still haven't gotten them back on). Like others have said mine has a hole in the top to get to the nut. I didn't have a big enough impact wrench so I had to use a rachet and breaker bar to get the nut off.  Once the nuts were off, I still had to get the bolts out.  They are pressed in with a keyway so they wont rotate when you tighten them.  I had to us an 8lb sledge to get the bolts out.. I'm going to support the frame so I can get under it to get the blades on, and the  nuts started.  Then I'll use a impact wrench to tighten the bolts.  They are suppose to be tightened to 650ft/lbs.  
In my case I'm not sure flipping the thing over would have helped at all.
Wedge