Whats the deal with 340s?

Yep. There's no substitute for cubic inches... longer strokes make more torque. .. advanced heads flow better... one could build a near 'perfect' engine... but with all the compromises the factory made, they still had a stout small block. Kudos to the engineers of 40+ years ago. Even in 72 and 73, they were a 'decent' motor... not the badass they were in 68/69/70.. but they still made a statement. Today's strokers with high flowing aluminum heads will smoke them, but 40ish years ago they held their own...