I am shooting for 15 mpg on the highway. I was planning on using Gibson headers with a aftermarket muffler. Also improvements in the airflow and fuel delivery. I was thinking of a good torque producing camshaft, 36lb injectors, and mild port work on the heads. Lastly, tuning the 411 pcm to optimize the efficiency of that setup.
Go Gibson headers, with 3" downpipes, to an H-pipe, to 2.75 or 3" all the way back. High-flow mufflers and no cats will go great with what you're doing.
Bankspowered98 on another forum claimed 430HP/667lb-ft with a .510/.540 cam, roller rockers, .30-over, compression bump (good idea), MSD box, CAI, larger throttle body (No clue where to get one), and full exhaust (full banks kit). He did not state if this was with a tune, but he had mentioned he was going to get another done for it. Later after the whipple he claimed 493/609. Odd numbers for 10lbs of boost and all of the rest of the work he did to it.
If it were me, and I was rebuilding the motor from the crank out, I would do just what he did. You'll probably need those 36lb injectors then.