In May of 1970, CAR CRAFT Magazine ran an article titled 'Econo Racer Test' which pitted the 4 strongest and cheapest performance cars against each other - here's the results:
#1 Duster 340 4sp w/3:91's = 14.22@99.88
#2 Swinger 340 3sp w/3:91's = 14.70@96.84
#3 Nova SS 350 4sp w/4:10's = 14.91@94.04
#4 Mach 1 351 4sp w/3:50's = 15.23@94.33
Then in April of '71, CAR CRAFT ran an article titled 'Drag Comparison' where it put the Demon 340 with the new 850cfm ThermoQuad up against a Hornet 360 and this is what it ran:
Stock form: 14.41@98.69mph
W/Headers: 13.61@104.52mph
Lots more 340 information, production numbers etc. here:
https://www.swinger340specials.ca/340-review