340 HP's vs headers

Well that and with some slight hogging out i can get 2.50" opening at the *** end. Damper is missing, going to drill n tap and plug those holes. My performer rpm doesnt have a heat riser that would tak advantage of a heat riser flap anyways. My question is am i gonna lose a lot of power with these over a set of headers on my stroker. I can live with a 40-50hp loss if i'm still in a low 400 hp range with the manifolds.