340 headers, or Dakota manifolds

iam getting ready to put my 340 in the valiant, and dont have the headers yet... thinking of putting in the dak manifolds until i can get a set of headers that will fit with power steering...the 340 is 68 340, 0.60 pistons purple cam 284/484, 8 3/4 3:55 sure grip. 727 trans, how much difference will headers make, over the dak manifolds....