Sorry this ref is coming so late in the game.

To my knowledge, there was only one 5' built and seeing it in person the other week, it does have the gear boxes added to the bottom.  It looks like all the rest was original.  The 32" was built for the fancy flying shots.  I didn't know they modded the fiver until I saw it.  Here's the video, but there are also other shots from the star wars exhibit that's been going around the last few years.

Star Wars Model Reference SantaAna 2012

StarWars Exhibit Model Ref 2012 Photos

And stills can be found here at my old website.

http://www.twinlitworlds.com/modelwerx/libraries/ref_sw_ships/?detectflash=false&