intake gasket questions

YR is once again spot on once again. I have to ask, thou, why are you using an action plus? The iron 340 manifold is better than it is, as the Weiand has 318 sized ports that extend deep into the manifold. If at all possible, switch to a performer RPM, an LD 340, or an iron intake. If you do continue to use a 318 size port manifold, a Fel-Pro 1243 gasket (273-318 size ports) may be a better option, but I would definitely GaskaCinch or Hi-Tack it into place on the manifold. A Weiand stealth may be a better choice, it has the same ports and design as an action plus but a square bore carb flange. Appearance wise, it looks like a taller version of an Edlbrock LD4B. I will compare the port to plenum arrangement to see how close they are. Whatever you choose to run, based on the symptoms you describe you should do what this article says.
http://www.hughesengines.com/Upload/TechArticles/INTAKE_MANIFOLD_SEALINGJULY2015.pdf