Nice to see my link above.
320hp for $6200? Where? You are talking bottem end work at that range, if you want reliability.
Do the engine work now. Pistons, valves, springs, studs, water injection . . .enough to get you to 300hp. You WILL want it.
How much does it take? All of it.
But, $6200 doesn't BEGIN to touch mine and I'm 'only' at 303.