Hello, I was just about to do a similar research about the "accurate" size of the Rebel "Gallofree" transport when a Google image search and in particular savmagoett's schematics led me to this thread.
Obviously being rather late to this party I wonder if it's okay to re-vitalize this rather interesting topic, alternately I'd be more than happy if a fellow fan or old fossil could direct me to a current one.
(I also have to voice concerns with Adywan's curving of the "first catch of the day" Star Destroyer Bridge - the images in SW The Blueprints on pages 124-125 and the production skill on page 126 - in color in the Empire of Dreams documentary - strongly suggest, IMHO, that flat bridge windows (corresponding with the conning tower of the large VFX Star Destroyer model built for ESB!) was an original studio set concept that survived at least in the "first catch of the day scene (even though it was actually photographed in the port alcove of the control deck set)
From what I read I concur with savmagoett's approach and methodology.
Rebel "Gallofree" Transport:
It appears that the process of overimposing the model of the ship in the foreground of the matte painting was erroneous (yielding the 26 m figure).
The two transports in the back (one probably lifted for repair works, hence the missing cockpit pod and aft landing gear?) look like sitting inside a much higher ice hangar compartment and seem bigger.
The ESB Sketchbook also had a size comparison page with the Rebel "Nebulon" Cruiser, the Falcon and the Rebel transport ship which looks like the 120 m figure (ROJ fleet fly-by) is accurate.
The ESB screenplay 4th draft from October 24, 1978 featured a scene inside the cockpit (pod):
"181. INT COCKPIT - REBEL TRANSPORT
The pilots are getting nervous, the captain leans over one.
I don't know if there's anyone left alive in there. Give it one more try.
Control unit 33, this is Transport XJ...we can't wait any longer..."
Apparently the cockpit pod must be large enough to accomodate at least three people, something also suggested in the ROJ novelization reffering to (transport ships converted into "fire ships") "crews abandoning their ships to an unknown fate".
small Corellian battleship (ROJ screenplay designation aka Rebel Blockade Runner and/or Corellian Corvette):
I'm not convinced with the 150 m figure. I had the opportunity to examine the original VFX model at the Marin County Fair back in 1988 (i.e. before the SW teaser poster was added to cover the doorframe - IIRC, 16 padding elements each - on the cockpit's starboard side) and my impression was that of a scale of 1:48.
However, IMHO, the actual element that determines the real size can only be the life-size escape pod's landing module from the Tunisian desert shoot matched against the escape pods on the "wings'" underside of Princess Leia's consular ship.
I'm currently not aware of a study examining this particular detail and the results that it would have on the overall in-universe length of this iconic SW ship.
Nevertheless, an "accurate" result inevitably has ramifications regarding the in-universe size of the Devastator- or Corellia-Class Star Destroyer featured in ANH because of the holding bay VFX composition.
size of regular Star Destroyer
I don't buy that all Star Destroyers have to share an equal length of 1 mile, because that particular figure was officially introduced for the large VFX model built for ESB.
On the contrary, the ROJ novelization explicitly mentions a "larger" Star Destroyer and having compared the conning tower proportions of the smaller ANH model vs. the bigger ESB model, my bet would be that the ANH model could be the "larger" one in-universe (ultimately pending on the most accurate length figure for the Blockade Runner).
Executor vs. nameless Super Star Destroyer of the Emperor
Both the ESB Sketchbook and the Art of ESB established that the name of Vader's Star destroyer seen in the film is Executor. It was further established that the conning tower of Executor is the same size as the one of a regular Star Destroyer (nicely visualized in the Imperial fleet's approach to Hoth) and the card of the ILM guys at the 1988 Marin County exhibit clearly stated the length of Executor to be 11 miles (the erroneous 5 mile figure comes from an unfortunate mis-transcription from Glut's ESB novelization into Velasco's SW guide, adopted by the folks at West End Games).
Based on my own and independent research I concur with savmagoett that the Falcon attached to the Avenger's conning tower in ESB confirms the official 1 mile length figure and that the corresponding, accurately dimensioned forward bridge is - indeed - the one briefly seen on the large conning tower VFX model in the scene with the Rebel Starcruiser flying overhead.
If I correctly followed the discussion in this thread, then Adywan has outruled this possibility because of the Tydirium fly-by scene in front of the Super Star Destroyer's coning tower in ROJ, suggesting a much larger conning tower (with the smaller VFX bridge model module).
Inevitable question: Can we be certain that the Super Star Destroyer in ROJ is - indeed - the Executor and not just the Emperor's personal and bigger Super Star Destroyer?