Scale differences between model manufacturers.

While dimensions may vary among manufacturers even today, a lot of the older Monogram kits (and the SBD first came out in the late '50s-early '60s) were roughly 1/4" scale. I don't think the kit designers were fanatical about getting the dimension exactly 1/48 scale, and several of the Monogram kits labeled 1/4" scale are actually a bit smaller - the T-28 Trojan comes to mind - but it didn't really matter much to the buyers back then. The "scale" gave them a rough idea of the size of the finished model. Most Monogram WWII kits and Lindberg jets of that era were " 1/4" scale" which was big enough to have rudimentary working parts (retractible landing gear, dropping bombs, folding wings, etc.) and passable, if not fantastic (in the classical sense) detail.

It is more than just scale variations.  Kits often have many other glaring inaccuracies.  Some kits are better than others, and I do think in general model companies are getting better.  And yes, some brands are better than others as well.  I think in these days of easy contact of mfgs, we do need to complain to companies. It is one thing to vote with your pocketbook, but even more effect is to vote with pocketbook but let mfgs know your unhappiness with offerings that are too bad in scale or details or whatever.

From several modeler's reviews, yes you can.  Google for Monogram Snaptite B-26 and you can read several reviews on the early B-26 which is what Kermit Week's and MAP's is.  The tail position glass is available from Squadron which has had it for many years.  Also google for the site, Flat Spins and Milkruns, where the author is building one.

Know nothing about Snaptite but can you get a decent model from it?  

FWIW,  the Monogram copyright is '88 on the instructions, '90 on the box.   The  Hasegawa is '94 box and instructions.   I think the experienced modeler out there knows the pitfalls better than I do but how else do you learn other than by buying the stuff.  Short cut to knowledge:  buy on ebay.

Another good example is Valom's 1/72 original B-26's which are very portly and long compared with the other B-26's like the Mono Snaptite and the Airfix B-26B.  The Snaptite is considered almost an accurate representation of an early B-26.

Even using today as a starting point kit makers still get easy stuff wrong. The Trumpeter and Wolfpack 1:48 T-38s have a noticable difference in fuselage length and these are relatively new tool kits. If I remember correctly the conclusion I read was the Trump was too long and the WP was too short. The Hasegawa 1:48 F-22 has ridges on the fuselage and wings that are inaccurate and look terrible. I believe while most kit makers do improve their research and acuracy on sequential kits they still get stuff wrong.

Sometimes I just have to laugh at the variance in size/shape of Sidewinder missiles between different kits, sometimes from the same manufacturer. (Different variant of missile notwithstanding)

Taking today as a starting point, are manufactures consistent in their scale representations?

It all depends upon the age of the kit and the accuracy of the plans used by the model companies to make their molds. But there can be a serious amount of variance in kits. Lest just start with figures and take it from there...