one thing the 383 definately has more of is torque... with a 4.25" bore, compared to 4.04" for the 340, and the 383 having a short stroke - in comparison to other big blocks ( 3.375 compared to 3.31 in a 340) 383's can REV... and cam selections are real close to small block specs... My father has owned a 70 chally 383 4 speed 3.23 rear since it was new, I own a 66 cuda that had a 340 ( now 360 ) auto, 3.23 and he would beat me every time... pull past me - I think thats why I put a dual quadded tunner rammed 360 in it... heh!
That being said - his brither and sister ( my uncle and aunt) had a 70 challenger 440 / 4bbl/ 4 speed 4.10 rear, and a 71 road runner 340 auto respectively... of course the 440 car with the 410's beat them all, BUT the 383 car would beat the 340 runner, altho from what I hear the runner could keep up, but not beat the 383.
If it were me - i'd go 383
