About the 340

340s have a smaller stroke, 3.313" to the 360s 3.58". The 340s have a larger bore 4.04" to the 360s, 4.00" bore

The 360 at a lower rpm then the 360 will.

The 340 is more desirable because they were all performance motors were as the 360 started out as a passenger car motor. The 360 was offered as a performance motor in 74 after the 340 was killed but because it was an emissions era motor it made less power then the early 340s which kinda earned it a bad rep.