Bore it to the max cubes, flat tops, headers, a 2 inch spacer, 500 CFM Holley, vortecs heads over regular production heads as they do flow much better but I dont know if they make a cast iron vortec manifold so you may be stuck with the other heads, cam change for sure, probably somewhere around a 268 high energy.
Ever heard of abrassive media porting? Looks just like a factor casting when done right, I've heard that it works wonders on heads and manifolds in these stock motor classes - Shhhh > anciet chinese secret.
Cp