Updated SPITFIRE HEADER INSTALL 63-66 A-body

on this subject,(curing the restrictive exhaust on early A bodys) It seems I read somewhere, sometime back that cast manifolds from certain years of Durangos,and maybe Daks could be used. I believe they said that they cleared everything well and flowed much better than the old 273s.
Anyone have the story on this, or maybe have done it?
Wish I could remember the source. I really would prefer good flowing factory type manifolds for the street. The best headers I ever had on anything, going back nearly 40 years were somewhat of a hassle just to keep tight. Can't be beat for performance tho!
BTW, I will be using a warm 360 so the 273 mans have to go.