Id say the 5.0 HO of the 80s would be a good side by side comparison of the early 70s 340 definitely the detuned smog 340. 5.0 HO was 225 horse the later 340 was 240 HP. early 340 has it beat though at 275 Horse. they both were "performance" engines.
But then the 5.0 is giving up 38 cubes. The 340 to 350 cube comparison is closer. The early 340s would probably win against most of the 350 cube comptition more often than not.
Used to be two friends in Edmonton, Alberta, Canada when we had the EIS facility. Both drag raced 340 Dusters. One had an automatic and the other was 4 spd. Winner depended solely on how they got of the lights. They could switch cars and the same happened. The General slush boxes were built for smooth Cadillac style shifts, not good for drag racing. Ford was in the middle.
The 5.0 HO was a bit slower when stock than the Camaro/Firechicken. However they sold like hotcakes as they were $10k less expensive. A couple of $k and they would leave the General in the dust. The 5.0 Mustangs were a couple of hundred pounds lighter, and that takes a lot of power to overcome. The Camaro/Firechickens had that, but a trip to a speed shop quickly cured that and brought power up to the Generals level. And that was giving up 48 cubes.