article from 2017... How Bad Did Mopar’s 340 beat Ford & Chevy?
For starters, if the 4bbl engine in the pic was used for the test, then it is not original specs because THAT engine has an AFB carb on it, original had an AVS.
The true test was back in the day. No 'rebuilding', no 'tuning'. PHR magazine pulled the small block engines from showroom cars & tested them to see if they made the adv HP. Results were published in Feb 69 issue, & I have the result page.
340 was the only engine that made it's adv rating of 275, but actually did better & made 295HP!!!
It also revved freely, was smooth & docile no bad habits.
Also tested: 350 Chebby, Olds W-31, Pontiac 350 HO, 351 Ferd. Here are the numbers. factory rating, then actual measured hp. 300, 240; 325, 280; 325,255; 290,210