I'm running the ported RHS Indy X from Brian, 340 XS274S SFT and my car picked up 4/10 from my ported j heads. The cam is not even taking full advantage of the heads potential. I can see how the OP did not pick up a ton of hp.
Brian does good work.
The RHS heads are a great starting point and really dont need much to make them perform. A good narrow 3 angle and light blending does the trick.
The j heads...well they are something not many have mastered or care to replicate the kind of work it takes ...so you have many who mostly end up with a set of 240 cfm heads and a ton casting still in the way. But that's not what this thread is about.
People need to remember 'a good cylinder head' can make a regular guy look like a porting god.