Any recommendations for building a '73 340?

You can use a 273, 318, or 340 forged crank. No need to swap K frame. Just need drivers side 340 mount LOL!! Get it balanced to your new bob weight anyways. 400 hp out of a 340 is easy. Mine current 340 dynoed 398 HP and it nothing real radical. 10:1 compression mildly ported 2:02 J heads, stock 340 forged crank and rods, LD340 intake, Holley 750 carb Comp XE284H cam .507/.510 lift I run 3:55s and drive the car all day city or country. Great street manors