Dyno shop tested 318

Sorry to see that. It sounded good when it was on the dyno. I'd keep that cam around for the 340.
For the exhaust, you might try adding a couple of 12" resonators before the mufflers, or after if you run it to the back. I have had good luck with Vibrant SS ones. They have a bottle style like I used or the ultra quiet version. Should knock down the amplitude and help with any drone.
Amazon.com : Vibrant Performance