tryna get close to 400 hp...Wanna work out my 973 casting 318 heads

Unless you are good a porting heads buying better ones will get you closer to your desired output. Since you are going with a flat top zero deck piston 360 heads would be a better choice. I ported a set of 318 heads for my dart and it took a long time and I removed a lot of material before I was happy with them. The same amount of work on a 360 head would yield a lot more flow. My motor is all stock besides the cam, ported heads and performer 318/360 with a thermoquad. If I had the flat tops you are running I would definitely go with at least J heads.