Back to the original question... 340s are easy to get in the 13s. When the rest of the car is set up to hook and accelerate. My '74, that had a '68 340 stock longblock and a stick, with 3.23s, would run 13.80s without the juice. All due respect 71, no way you need all that improved fuel delivery for any system under 200hp. Retard the timng 2° for every 100hp rated, and drop the fuel pressure to 4psi, and I ran 9 series Champions in it with a Jacobs ignition. That's it. That car was fed by a factory 5/16 line, and AC Delco stock replacement fuel pump, and a $6 Purolator pressure regulator to drop the limne pressure from 5.5psi to 4. With the 175hp plate on it, it went 12.50s, and I never used it in 1st. All runs were with Sonic Turbos (lol old school) and Dunlop GT Qualifier Radials. That engine had a Comp 268H High Energy cam, and a stock Tquad and Tquad intake. I did tune the heck out of it. In any event, the 340 needs gear, and static compression, and then it wakes up. No reason why a pretty much stock long block 340 can't touch the 13s with headers, better tires, a modern cam, and a rear gear steeper than 3.55s. You would need a convertor too. 340s dont have the highest torque figures. They like to live above 3K. I used to side step the clutch at 3200, and shift at 6000. If the car is not numbers matching and there is money enough to do a performance rebuild on that 340, go to 416. It's not much more, and the result is the ultimate street smallblock.
