"I'm not sure to what you're referring in your query ("whether this line is authentic"), but if it's to the "BASIC SPECIFICATIONS..." description in the script, I can assure you that it's transcribed correctly."
Thanks for the extra effort, but now I'd like to hear the whole story.
So what are we looking at?
A) A screenplay writer that wanted to leave a footprint in the Star Trek Universe by being the first to put the Enterprise
in a "Constitution Class" (He wouldn't be the the first as the early novel writers tried to pigeonhole the Enterprise
in a "Constellation Class" which makes the overused "Connie" rather debatable since that was the nickname for Lockheed's Constellation airplane: http://en.wikipedia.org/wiki/Lockheed_Constellation
I can't help but it appears too many people were clearly influenced by the US frigates USS Constellation
(launched September 7, 1797) and USS Constitution
(launched October 21, 1797). Of course the first frigate was the (USS) United States
which adds credibility to the "Starship Class" (e.g. "United Star Ship Republic")
B) A producer (Bob Justman) with amnesia (because "Constitution" isn't on his name proposal list from 9-8-1967) and delusion ("Enterprise Starship Class")?