If you check out some of the Aussie forums, they recommend only upgrading the intake valve to 1.84" and the exhaust valves to 1.56" maximum. The crossflow intake valve is the restriction for flow, not the exhaust side. These size valves will support 400Hp in a NA crossflow. The crossflow engine can also tolerate higher CRs than our stock cast iron, and it likes long duration cams but not dual pattern ones.
If you stay with a carb or throttle body, purchase an Aussiespeed intake. Their intakes, either 2Bbl or 4Bbl, only have a 3% variance between runners. They are great intakes. I have a 4Bbl Aussiespeed intake that I'm planning to use (once I get it from Bayrunner).