Rebuilding engine/ head gasket compression question

ok i've looked at the kb107's before actually. What is the advantage to flat over dome and dish? If my memory serves me correct, you have answered a few of my engine questions before, rumble. I was planning on building a streetable motor with 350+ hp. I've so far managed to gather an air gap intake, 650 holley, mopar purple cam and lifters 429"/.444" lift 268/276 duration pn4452782, proform roller rockers, oh and some nice shiney chrome edelbrock valve covers :) should i get new valve springs? what pushrods? man this whole engine thing is spendy. i havnt even touched the brakes, rear end and tranny yet. Thanks a ton for the info