Sounds like a great engine combination. My recommendation. Finish breaking in the engine, then do a power tune on a dyno. You may be surprised at the difference this will make. Also ... was the camshaft install correct for the power...did the front pully get installed in the proper position for the power band you are looking for? (how many keys were in the timing chain cam gear...this will tune the cam for the perfomance needed). Check a local hot rod shop for the details.
First recommendation after that...port the exhaust ports to match the gasket...don't go in much over an inch. Second recommendation...port and polish.
The 340 in my cuda gets 350 hp to the ground with 323 gears and a 833 4 speed. RPM air gap, X heads, Edelbrock 750, 1 3/4 inch exhaust and a good cam. Ignition is a Crane Digital MSD box. Try a power tune.