1973 340 Cam advice

a couple of thoughts...your valve springs are probably stock pieces having a damper inside the single wound spring.Your intake is fine and any 600 cfm carb will be good.
With 2.94 or 3.23 i'd select a 204 / 214 .429 / .444 cam.(Nearly every company makes one) and you will break the tires loose easily from a dead stop and pull hard from 1200 rpm to about 4800.You'll have a ball on the street to well past legal speeds with this combination.