Extra hp out of my 340.

Pretty much agree with the suggestions to leave the cam alone - depending of course on your real objective.
340 Hp is very respectible for a stock engine -
The one item that will help power for the entire rpm range will be extractors.
Even changing the intake manifold will likely somewhat compromise the bottom end - although you can easily cover that with converter, or make up for some it with extractors and carb (idle circuit) tuning.
See this post for a dyno comparison graph:
Edelbrock LD4B
There's a much more recent magazine test of a stock 340 with similar results, although higher numbers.
I'm going to presume by your Hp that there was no falling off at the top end due to valve float. You may pick up some high rpm power with a Mopar Performance "tach drive" distributor - but it has no vacuum advance so it will hurt fuel milage.
So my suggestion is spend the time and money on the extractors first. Intake depending on what you want.

If there aren't any extractors down under for the left hand drive models, then either Doug's or TTI's from here (stateside) are probably the best of the mass produced headers. If you have someone do custom, especial in stainless, that's a great option even though expensive. Take the time to match the top and sides of the ports.