EF head (94AB)or 94DT EF tickford head both flow the most of any 4L head. Mate it to an AU block as rotating assy is lighter and better for revs. Stay away from EL xr6 or el hybrid motors, they have absolutely trash ports that flow only marginally better than an old 250xflow.
If you port the head have it flowed and chose a cam accordingly, there is a company that makes off the shelf Carby manifolds however they flow around 30cfm less than an EF head and flow is uneven across runners.
Best bet would be a custom manifold. EA CPI flows like shit unless anyone has flow figures to debunk that?
Best headers for speedway would likely be pacemaker 4480?s or If you can track down a set of Jim mock race series headers they work well (I?ve used both).
If you want the best performance, CVE performance in Melb will give the best advice. He builds some quick 4L?s. One went [email protected] in an EA 5sp. Good luck.