I'll assume that Dragon is using their Opel Blitz 3ton truck kit as the base for this new gun-truck edition - and believe that we can probably safely conclude that this vehicle AS KITTED was NOT over-loaded by carrying the 2cm FlaK 38, ammo, and crew. Whether or not the mentioned booster springs were added. (Are those springs depicted in Dragon's Opel kit?)
Maybe someone out there actually KNOWS whether there really was one of these built and used... I suspect that there was ONE - and that the D has found some pic(s) of it. Dragon has done many one-offs and very rare vehicles over the years, and this is surely one of those rarities. As 3ton Opels were common trucks, it does seem likely that the truck used would have been that 3-tonner - but was it a 4x2 (more common) or a 4x4 (more capable and versatile) truck? Dragon is modeling it as a 4x2, but maybe that's because they have all that already made and available?
Pics of real Opels-w-2cm FlaK 38 are pretty common - a fair number of these were "built" by units throughout the war - almost all of which were single-gun conversions, with or without shields. And both 4x2 and 4x4 trucks were used.
The field conversion was common enough that a special "FlaK-sled" kit was developed and issued to facilitate using 2cm FlaK 38 in cargo trucks - maybe this kit will include that item, too?
There are, on the other hand, very few pics showing any sort of armored Opel Blitz... A couple that I've seen show a fairly-"formal-looking" (so, built at an equipped facility as versus in some unit shop) armored front end with a specially-built bed for a FlaK gun - this truck is NOT the one being kitted. I did some Google searches and could not find anything which looked like the kit - only means that I couldn't find a pic, of course! - but armored Opels were extremely rare.
There was a 1/72 scale "MAC" kit out several years ago of what looks to be this same or very similar configuration - it shows up in build pics on the web.
Given as this thing was a rarity or maybe a one... A photo or 3 would be of GREAT help in building it to best represent real history - probably more-accuracy-minded modelers will find themselves constrained in painting it up...
For others, it is a cool-looking truck, regardless of kit versus historical details. I plan on getting it when it boils off its new-release / rare kit price!