Few suggestions;
If you tear into it, change rod bolts to ARP and get rods resized.
Keep the cam and intake and headers you have. Buy a set of Open chambered Oval port heads from a 402 that have the same combustion chamber size you have now. That way you can use your same pistons. Get 2.19 Inatke and 1.88 exahust vlvs put in them with Hardned seats if they don't have them. a few did and most didn't. That should pick you up some without much money spent.
Or;
Keep your cam and rods and buy a 454 block and crank, cast is ok to above 600 hp and above 7,500 rpm. Buy a set of oval port 049 or 781 castng heads you can run them as they are with some pocket porting but it is better to change valves to 2.19 and 1.88 get a set of pistons to give you appx 10.50. - 1 compression, and really enjoy more torque and power and at the same time let the know it alls see that you still have the same old engine and just did some better tuning on it. A good single plane intke would help too. You can get Team G 's on ebay for maybe $75 to $100 dollars and they work good.
Ed