Nick's Garage has a nice video of dyno testing a 1970 340 for a 'Cuda.
Engine made 335 HP initially. With tuning it pulled 340.2 HP and 345.7 f-p of torque.
Nick tested a modified 340 with E-brock heads, AirGap, Holley DP, Cam was 0.525" lift, Engine made 395 HP after 10 pulls and tuning.
My 340 for my '68 FB FS will be similar but with a Purple Shaft 280°/0.480" cam for more streatability. I would be happy with 340 HP.