dyno numbers from my 340 just for reference

That is really good for a stock 340 , REALLY good , in fact you have one of the strongest stock 340 I've seen. But then again your taking a guess on the internals unless you tore it down to inspect .
Mine makes 412HP 400 TQ , 355 HP , 343 TQ at the rear wheels , but it's not stock , 10.5:1 Mahle ceramic coated pistons .30 over , forget the cam specs , but it is lumpy , heads are cleaned up ported with headman tight tube headers with 2 1/2 " mandrel bend pipes and a 750 eddy carb and edelbrock air gap , automatic and 3:55 gears