I had a 390 Holley on an Offy 4BBL manifold (using an adapter) on an 276 ci 8BA with an Isky MAX-1 in a '36 3-window about 30 years ago; it was the first hi-performance flathead that I built. It ran fine, but it wasn't a "world-beater". I don't think this had anything to do with those components. More than likely, it was due to my lack of flathead knowledge on combustion chamber dynamics and ignition systems. I'd like to do it over again these days, but I am too committed to using earlier components.