Will headers hurt exhuast flow?

[Mccoleman830]

I finally found c.a.r.b. legal full length headers from Hedman for my 78 K-15 PN# 66231. My question is, will long tube headers be more restrictive over my cast iron manifolds when routed into the factory "Y" pipe? It must be routed into the factory "Y" pipe because it has to be smog legal. I was told that since I can't run "true duels" then there isn't any point to buy headers. The reason why I want headers is to replace my cracked manifolds i currently have. Thanks for your help.